U.S. patent application number 10/663060 was filed with the patent office on 2004-03-18 for high-strength bolted connection structure with no fire protection.
Invention is credited to Kubota, Shin, Okada, Tadayoshi, Uno, Nobuyoshi.
Application Number | 20040050013 10/663060 |
Document ID | / |
Family ID | 31996152 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040050013 |
Kind Code |
A1 |
Okada, Tadayoshi ; et
al. |
March 18, 2004 |
High-strength bolted connection structure with no fire
protection
Abstract
The present invention provides a high-strength bolted connection
structure for realizing a steel structure with no fire protection,
which is capable of adequately assuring high-temperature strength
of the connection in a high temperature region of 650.degree. C.,
and which does not depend on a fire protection or protective
structure using fire resistant material, wherein
ultra-high-strength bolts having excellent fire resistance and
excellent resistance to delayed fracture are used, which bolt have
a tensile strength at room temperature (TS) of 1200 N/mm.sup.2 or
higher, and satisfies the relation that the shear proof stress at
high temperature of 650.degree. C. (b.tau.t) is not less than
(coefficient of slip at room temperature (.mu.).times.design bolt
tension (N.sub.0))/(safety factor for long term load
(.nu.).times.cross-sectional area of bolt shank (bAs)).
Inventors: |
Okada, Tadayoshi;
(Futtsu-shi, JP) ; Uno, Nobuyoshi; (Futtsu-shi,
JP) ; Kubota, Shin; (Chiyoda-ku, JP) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Family ID: |
31996152 |
Appl. No.: |
10/663060 |
Filed: |
September 12, 2003 |
Current U.S.
Class: |
52/848 |
Current CPC
Class: |
E04B 1/2403 20130101;
E04B 2001/2418 20130101; E04B 2001/2457 20130101; E04B 2001/2454
20130101; E04C 3/06 20130101; E04C 3/32 20130101; E04B 2001/2415
20130101 |
Class at
Publication: |
052/726.2 |
International
Class: |
E04C 003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2002 |
JP |
2002-266534 |
May 30, 2003 |
JP |
2003-155127 |
Claims
1. A high-strength bolted connection structure with no fire
protection, the high-strength bolted connection structure having
the fire resistance of a steel structure comprising columns and/or
beams, characterized in that ultra-high-strength bolts having a
bolt tensile strength (TS) at room temperature of 1200 N/mm.sup.2
or higher and excellent fire resistance with a bolt shear proof
stress (b.tau.t) at 650.degree. C. satisfying the relation
<1> below, are used:
b.tau.t.gtoreq..mu..times.N.sub.0/(.nu..times.bAs) <1>where
b.tau.t: bolt shear proof stress at high temperature (N/mm.sup.2)
b.tau.t=TSt/{square root}3 TSt: tensile strength of the bolts at
high temperature (N/mm.sup.2) .mu.: coefficient of slip at room
temperature N.sub.0: design bolt tension (N) .nu.: safety factor
for long-term load bAs: cross-sectional area of bolt shank
(mm.sup.2).
2. A high-strength bolted connection structure with no fire
protection according to claim 1, wherein, in said high-strength
bolted connection structure, the long term allowable shear force
(Qs) of said beam at room temperature satisfies the relation
<2> below:
Qs.ltoreq.{ns.times.b.tau.+(nf-ns).times.b.tau.t}.times.bAs
<2>where Qs: long term allowable shear force of the beam at
room temperature (N) Qs=fs.times.Ab fs: long term allowable shear
proof stress of the beam (N/mm.sup.2) Ab: cross-sectional area
(mm.sup.2) ns: number of tension bolts in the floor slab on upper
flange side of the beam b.tau.: shear proof stress of bolt at room
temperature (N/mm.sup.2) b.tau.=TS/{square root}3 TS: tensile
strength of bolt at room temperature (N/mm.sup.2) nf: number of
tension bolts on the upper flange side of the beam b.tau.t: shear
proof stress of bolt at high temperature (N/mm.sup.2)
b.tau.t=TSt/{square root}3 TSt: tensile strength of bolt at high
temperature (N/mm.sup.2) bAs: cross-sectional area of bolt shank
(mm.sup.2).
3. A high-strength bolted connection structure with no fire
protection according to claim 1 or 2, wherein said high-strength
bolted connection structure is composed of sets of a high-strength
bolt, a nut, and a washer, and joint metals, and wherein said nut
and washer are a general structural hexagon nut and a structural
high strength plain washer for which no fire resistance is
provided.
4. A high-strength bolted connection structure with no fire
protection according to claim 1 or 2, wherein said high-strength
bolted connection structure is composed of sets of high strength
bolt, a nut, and a washer, and joint metals, and wherein a part or
all of said joint metals are formed of steel material having an
assured high-temperature strength.
5. A high-strength bolted connection structure with no fire
protection according to claim 1 or 2, wherein, in said
high-strength bolted connection structure, a part or all of said
columns and/or beams used are formed of steel material having an
assured high temperature strength.
6. A high-strength bolted connection structure with no fire
protection according to claim 1 or 2, wherein said high-strength
bolt is a ultra-high-strength bolt which contains, in % by weight,
C: 0.30.about.0.45%, Si: less than 0.10%, Mn: more than
0.40%.about.less than 1.00%, P: less than 0.010%, S: 0.010% or
less, Cr: 0.5% or more.about.less than 1.5%, Mo: more than
0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or less,
with the balance being Fe and unavoidable impurities, and which has
excellent fire resistance and resistance to delayed fracture such
that following relations <3>, <4> are satisfied:
TS.ltoreq.(1.1.times.T+850) <3>TS.ltoreq.(550.times.Ceq+1000)
<4>where TS: tensile strength of the high strength bolt at
room temperature (N/mm.sup.2) T: tempering temperature (.degree.
C.) Ceq: carbon equivalent (%)
Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
7. A high-strength bolted connection structure with no fire
protection according to claim 3, wherein said high-strength bolt is
an ultra-high-strength bolt which contains, in % by weight, C:
0.30.about.0.45%, Si: less than 0.10%, Mn: more than
0.40%.about.less than 1.00%, P: less than 0.010%, S: 0.010% or
less, Cr: 0.5% or more.about.less than 1.5%, Mo: more than
0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or less,
with the balance being Fe and unavoidable impurities, and which has
excellent fire resistance and resistance to delayed fracture such
that following relations <3>, <4> are satisfied:
TS.ltoreq.(1.1.times.T+850) <3>TS.ltoreq.(550.times.Ceq+1000)
<4>where TS: tensile strength of the high strength bolt at
room temperature (N/mm.sup.2) T: tempering temperature (.degree.
C.) Ceq: carbon equivalent (%)
Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
8. A high-strength bolted connection structure with no fire
protection according to claim 4, wherein said high-strength bolt is
an ultra-high-strength bolt which contains, in % by weight, C:
0.30.about.0.45%, Si: less than 0.10%, Mn: more than
0.40%.about.less than 1.00%, P: less than 0.010%, S: 0.010% or
less, Cr: 0.5% or more.about.less than 1.5%, Mo: more than
0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or less,
with the balance being Fe and unavoidable impurities, and which has
excellent fire resistance and resistance to delayed fracture such
that following relations <3>, <4> are satisfied:
TS.ltoreq.(1.1.times.T+850) <3>TS.ltoreq.(550.times.Ceq+1000)
<4>where TS: tensile strength of the high strength bolt at
room temperature (N/mm.sup.2) T: tempering temperature (.degree.
C.) Ceq: carbon equivalent (%)
Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
9. A high-strength bolted connection structure with no fire
protection according to claim 5, wherein said high-strength bolt is
an ultra-high-strength bolt which contains, in % by weight, C:
0.30.about.0.45%, Si: less than 0.10%, Mn: more than
0.40%.about.less than 1.00%, P: less than 0.010%, S: 0.010% or
less, Cr: 0.5% or more.about.less than 1.5%, Mo: more than
0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or less,
with the balance being Fe and unavoidable impurities, and which has
excellent fire resistance and resistance to delayed fracture such
that following relations <3>, <4> are satisfied:
TS.ltoreq.(1.1.times.T+850) <3>TS.ltoreq.(550.times.Ceq+1000)
<4>where TS: tensile strength of the high strength bolt at
room temperature (N/mm.sup.2) T: tempering temperature (.degree.
C.) Ceq: carbon equivalent (%)
Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-strength bolted
connection structure with no fire protection that can be applied to
the case of a high-strength bolted connection of a column to a beam
member or to beam members constituting a steel structure for which
fire resistance is required, directly or indirectly, via a join
metal such as a T-shaped join metal or a splice-plate. The
high-strength bolted connection structure with no fire protection
of the present invention includes both a friction type
high-strength bolted connection structure with no fire protection
and a tension-type high-strength bolted connection structure with
no fire protection.
BACKGROUND ART
[0002] In a steel structure for which fire resistance is required,
when the constituent pillars or beam members are exposed to high
temperature at the time of a fire and their strength is lowered,
they can no longer function as the steel structure adequately.
Thus, conventionally, such steel members have been protected from a
high temperature by means of a complicated fire protection provided
on the steel members themselves or by provision of protective
structure using fire resistant material.
[0003] However, provision of such a fire protection on steel
members or a protective structure for steel members leads
inevitably to an increase in material cost as well as in
construction cost. Therefore, recently, several fire-resistant
steels having excellent high-temperature strength have been
developed which steels have an increased high-temperature strength
for a time period corresponding to duration of a fire, and which
are mainly directed to realization of a steel structure with no
fire protection. Thus, the same excellent high-temperature strength
is also required for a high-strength bolted connection of steel
members formed of such fire resistant steels.
[0004] As regards high strength bolts and nuts, Japanese Patent
Publication No. 02-247355 (claim 1, Table 7 and FIG. 1), for
example, has proposed a Mo-added steel, suitable to be used for
bolts and nuts, which has a bolt tensile strength of 1000
N/mm.sup.2 or higher at room temperature, and has excellent
high-temperature strength at temperature of 600.degree. C. or
higher. However, this steel does not have adequate high-temperature
strength, and requires addition of expensive alloy elements such as
Ni, V, etc. in order to obtain increased high-temperature strength,
which gives rise to the problem of increased cost.
[0005] Japanese patent Publication No. 05-51698 (claim 2 and Table
2) and Japanese patent Publication No. 05-98389 (claim 1 and Table
2) have proposed a steel material, suitable to be used for bolts
and nuts, which has a bolt tensile strength of 1000 N/mm.sup.2 or
higher at room temperature, and has yield strength of 400
N/mm.sup.2 or higher at temperature of 600.degree. C. However, this
steel requires addition of special elements such as Nb, W, etc.,
and thus gives rise to the problem of increased cost. Also, high
temperature strength is still insufficient.
[0006] On the other hand, although, in the case of above-described
conventional high-strength bolts having known fire resistance, the
bolt tensile strength may sometimes become as high as about 1100
N/mm.sup.2, there is another problem, that is, the problem of
"delayed fracture", that, even if the bolt is used under stress
equal to or lower than the yield stress, after a certain time
period has elapsed from clamping, the bolt may suddenly break,
which does not permit the bolt to be used as an important joint
member of a steel structure. Thus, one is forced to adopt
conventional bolt tensile strength of about 1000 N/mm.sup.2 as the
upper bound, so that the number of bolts and length of the joint
metal member is inevitably increased. Thus, there is still a strong
need for a reduction in cost as well as a reduction in the work
execution time.
[0007] The high-strength bolts and nuts as disclosed in
above-described known literature are all characterized by the
amount of added alloy elements, and in addition to the essential
problem that, in order to improve fire resistance, the amount of
expensive additive elements, and hence the material cost, must
increase, there is another problem that the phenomena of delayed
fracture may occur.
[0008] It is therefore an object of the present invention to
provide a high-strength bolted connection structure with no fire
protection using an ultra-high-strength bolt which does not require
fire protection or a protective structure of refractory material
and which can resolve the problem of delayed fracture and can
assure adequate strength at a temperature of 650.degree. C. while
allowing a reduction in material cost as well as reduction in the
work execution time.
SUMMARY OF THE INVENTION
[0009] In order to attain above object, the present invention
provides (1).about.(9) as described below.
[0010] (1) A high-strength bolted connection structure with no fire
protection, being a fire resistant high-strength bolted connection
structure of a steel structure having columns and/or beams,
characterized in that an ultra-high-strength bolt with excellent
fire resistance is used, which bolt has bolt tensile strength (TS)
of 1200 N/mm.sup.2 or higher at room temperature and which has a
bolt shear proof stress (b.tau.t) at 650.degree. C. satisfying
equation <1> below:
b.tau.t.gtoreq..mu..times.N.sub.0/(.nu..times.bAs) <1>
[0011] where
[0012] b.tau.t: bolt shear proof stress at high temperature
(N/mm.sup.2)
[0013] b.tau.t=TSt/{square root}3
[0014] TSt: bolt tensile strength at high temperature
(N/mm.sup.2)
[0015] .mu.: coefficient of slip at room temperature
[0016] N.sub.0: design bolt tension (N)
[0017] .nu.: safety factor for long term load
[0018] bAs: cross-sectional area of bolt shank (mm.sup.2).
[0019] (2) A high-strength bolted connection structure with no fire
protection according to (1), wherein, in said high-strength bolted
connection structure, the allowable long term shear force (Qs) of
said beam at room temperature satisfies equation <2>
below:
Qs.ltoreq.{ns.times.b.tau.+(nf-ns).times.b.tau.t}.times.bAs
<2>
[0020] where
[0021] Qs: allowable long term shear force of the beam at room
temperature(N)
[0022] Qs=fs.times.Ab
[0023] fs: allowable long term shear proof stress of the beam
(N/mm.sup.2)
[0024] Ab: cross-sectional area of the beam (mm.sup.2)
[0025] ns: number of tension bolts in the floor slab on the upper
flange side of the beam
[0026] b.tau.: shear proof stress of the bolt at room temperature
(N/mm.sup.2)
[0027] b.tau.=TS/{square root}3
[0028] TS: tensile strength of the bolt at room temperature
(N/mm.sup.2)
[0029] nf: number of tension bolts on the upper flange side of the
beam
[0030] b.tau.t: shear proof stress of the bolt at high temperature
(N/mm.sup.2)
[0031] b.tau.t=TSt/{square root}3
[0032] TSt: tensile strength of the bolt at high temperature
(N/mm.sup.2)
[0033] bAs: cross-sectional area of bolt shank (mm.sup.2).
[0034] (3) A high-strength bolted connection structure with no fire
protection according to (1) or (2), wherein said high-strength
bolted connection structure is composed of a set of a high-strength
bolt, a nut and a washer, and joint metal, and wherein said nut and
washer are a general structural hexagon nut and a structural plain
washer each having no defined fire resistance.
[0035] (4) A high-strength bolted connection structure with no fire
protection according to (1) or (2), wherein said high-strength
bolted connection structure is composed of a set of high-strength
bolt, a nut and a washer, and joint metal, and wherein a part or
all of said joint metal is formed of a steel material having an
assured high temperature strength.
[0036] (5) A high-strength bolted connection structure with no fire
protection according to (1) or (2), wherein, in said high-strength
bolted connection structure, a part or all of said columns and/or
beams used are formed of a steel material having an assured
high-temperature strength.
[0037] (6) A high-strength bolted connection structure with no fire
protection according to (1) or (2), wherein said high-strength bolt
contains, in % by weight, C: 0.30.about.0.45%, Si: less than 0.10%,
Mn: more than 0.40%.about.less than 1.00%, P: less than 0.010%, S:
0.010% or less, Cr: 0.5% or more.about.less than 1.5%, Mo: more
than 0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or
less, with the balance being Fe and unavoidable impurities, and
wherein said high-strength bolt is an ultra-high-strength bolt
having excellent fire resistance and a delayed fracture resistance
satisfying equations <3> and <4> below:
TS.ltoreq.(1.1.times.T+850) <3>
TS.ltoreq.(550.times.Ceq+1000) <4>
[0038] where
[0039] TS: tensile strength of the high strength bolt at room
temperature (N/mm.sup.2)
[0040] T: tempering temperature (.degree. C.)
[0041] Ceq: carbon equivalent (%)
[0042] Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
[0043] (7) A high-strength bolted connection structure with no fire
protection according to (3), wherein said high-strength bolt
contains, in % by weight, C: 0.30.about.0.45%, Si: less than 0.10%,
Mn: more than 0.40%.about.less than 1.00%, P: less than 0.010%, S:
0.010% or less, Cr: 0.5% or more.about.less than 1.5%, Mo: more
than 0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or
less, with the balance being Fe and unavoidable impurities, and
wherein said high-strength bolt is an ultra-high-strength bolt
having excellent fire resistance and a delayed fracture resistance
satisfying equations <3> and <4> below:
TS.ltoreq.(1.1.times.T+850) <3>
TS.ltoreq.(550.times.Ceq+1000) <4>
[0044] where
[0045] TS: tensile strength of the high strength bolt at room
temperature (N/mm.sup.2)
[0046] T: tempering temperature (.degree. C.)
[0047] Ceq: carbon equivalent (%)
[0048] Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
[0049] (8) A high-strength bolted connection structure with no fire
protection according to (4), wherein said high-strength bolt
contains, in % by weight, C: 0.30.about.0.45%, Si: less than 0.10%,
Mn: more than 0.40%.about.less than 1.00%, P: less than 0.010%, S:
0.010% or less, Cr: 0.5% or more.about.less than 1.5%, Mo: more
than 0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or
less, with the balance being Fe and unavoidable impurities, and
wherein said high-strength bolt is an ultra-high-strength bolt
having excellent fire resistance and a delayed fracture resistance
satisfying equations <3> and <4> below:
TS.ltoreq.(1.1.times.T+850) <3>
TS.ltoreq.(550.times.Ceq+1000) <4>
[0050] where
[0051] TS: tensile strength of the high strength bolt at room
temperature (N/mm.sup.2)
[0052] T: tempering temperature (.degree. C.)
[0053] Ceq: carbon equivalent (%)
[0054] Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
[0055] (9) A high-strength bolted connection structure with no fire
protection according to (5), wherein said high-strength bolt
contains, in % by weight, C: 0.30.about.0.45%, Si: less than 0.10%,
Mn: more than 0.40%.about.less than 1.00%, P: less than 0.010%, S:
0.010% or less, Cr: 0.5% or more.about.less than 1.5%, Mo: more
than 0.35%.about.less than 1.5%, V: more than 0.3%.about.1.0% or
less, with the balance being Fe and unavoidable impurities, and
wherein said high-strength bolt is an ultra-high-strength bolt
having excellent fire resistance and a delayed fracture resistance
satisfying equations <3>, <4> below:
TS.ltoreq.(1.1.times.T+850) <3>
TS.ltoreq.(550.times.Ceq+1000) <4>
[0056] where
[0057] TS: tensile strength of the high strength bolt at room
temperature (N/mm.sup.2)
[0058] T: tempering temperature (.degree. C.)
[0059] Ceq: carbon equivalent (%)
[0060] Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
BRIEF DESCRIPTION OF DRAWINGS
[0061] FIG. 1 is a perspective view useful for explaining an
example of a friction-type high-strength bolted connection
structure of beam members to be connected according to the present
invention;
[0062] FIG. 2 is a sectional view useful for explaining an example
of a friction-type high-strength bolted connection structure of
brace members to be connected according to the present
invention;
[0063] FIG. 3 is a partial perspective view useful for explaining
an example of a friction-type high-strength bolted connection
structure of beam to T-shaped joint metals to be connected and a
tension-type high-strength bolted connection structure of column to
T-shaped joint metals to be connected according to the present
invention;
[0064] FIG. 4(a) is a partial sectional view useful for explaining
an example of a friction-type high-strength bolted connection
structure of beam to T-shaped joint metals and a tension-type
high-strength bolted connection structure of column to T-shaped
joint metals of FIG. 3;
[0065] FIG. 4(b) is a partial plan view useful for explaining FIG.
4(a);
[0066] FIG. 5 is a partial sectional view useful for explaining an
example of a friction-type high-strength bolted connection
structure of beam to T-shaped joint metals and a tension-type
high-strength bolted connection structure of column to T-shaped
joint metals in a case of a floor slab disposed on the upper part
of the beam flange;
[0067] FIG. 6 is a view useful for explaining the relation between
the tempering temperature and tensile strength (TS) of steel and
the presence or the absence of a delayed fracture;
[0068] FIG. 7 is a view useful for explaining the relation between
the carbon equivalent (Ceq %) and tensile strength (TS) of steel
and the presence or the absence of a delayed fracture;
[0069] FIG. 8 is a view useful for explaining the relation between
test temperature and shear proof stress (TS/{square root}3) (in the
case of M22 bolts);
[0070] FIG. 9 is a view useful for explaining the relation between
test temperature and shear proof stress (TS/{square root}3) (in the
case of M16 bolts);
[0071] FIG. 10 is a view useful for explaining the relation between
test temperature and shear proof stress (TS/{square root}3) (in the
case of M20 bolts);
[0072] FIG. 11 is a view useful for explaining the relation between
test temperature and shear proof stress (TS/{square root}3) (in the
case of M24 bolts);
[0073] FIG. 12(a) is a partial sectional view useful for explaining
an example of tension-type high-strength bolted connection
structure of a column-beam provided with a floor slab (in the case
of two bolts for T-shaped joint metal in the floor slab);
[0074] FIG. 12(b) is a side view useful for explaining the T-shaped
joint metal of FIG. 12(a);
[0075] FIG. 12(c) is a plan view useful for explaining FIG.
12(a);
[0076] FIG. 13(a) is a partial sectional view useful for explaining
an example of tension-type high-strength bolted connection
structure of a column-beam provided with a floor slab (in the case
of four bolts for T-shaped joint metal in the floor slab);
[0077] FIG. 13(b) is a side view useful for explaining the T-shaped
joint metal of FIG. 13(a); and
[0078] FIG. 13(c) is a plan view useful for explaining FIG.
13(a).
THE MOST PREFERRED EMBODIMENT
Description of the Embodiments of the Invention
[0079] The present invention is directed to a high-strength bolted
connection structure, that is, a friction-type high-strength bolted
connection structure and a tension-type high-strength bolted
connection structure. The invention uses ultra-high-strength bolts
which can assure adequate strength (shear proof stress) at room
temperature and at high temperature of 650.degree. C., and which do
not give rise to the problem of delayed fracture. Thus, the
invention allows the number of bolts to be decreased and the length
of joint metal to be reduced so that the overall cost and the work
execution time can be reduced, and a high-strength bolted
connection structure with no fire protection can be realized that
does not depend on a refractory covering or a protective structure
using a refractory material.
[0080] A high-strength bolted connection structure, which includes
a friction-type high-strength bolted connection structure and a
tension-type high-strength bolted connection structure, is to be
designed, in accordance with "Guide for design and work execution
of high-strength bolted connection" published in 1973 and amended
in 1993 by Architectural Institute of Japan, such that a
friction-type connection and a tension-type connection are treated
independently of each other in long-term design at room temperature
and in anti-seismic design. Therefore, in the present invention,
too, the high-strength bolted connection structure at high
temperature will be described separately for the two types of
connection structure, and the high-strength bolted connection
structures with no fire protection, that is, a friction-type
high-strength bolted connection structure with no fire protection
and a tension-type high-strength bolted connection structure with
no fire protection, are provided in accordance with the concept of
verification of fire resistant security of respective types of
connection.
[0081] In the present invention, both in the case of a
friction-type high-strength bolted connection structure and in the
case of a tension-type high-strength bolted connection structure,
the high-strength bolted connection structure with no fire
protection is realized basically by using ultra-high-strength bolts
which have a bolt tensile strength at room temperature of not less
than 1200 N/mm.sup.2 and not more than 1600 N/mm.sup.2 and which
have excellent shear proof stress at 650.degree. C., that is,
excellent fire resistance and excellent resistance to delayed
fracture (including torshear-type high-strength bolts, hereinafter
referred to as "ultra-high-strength bolts").
[0082] A steel material as disclosed, for example, in Japanese
Patent Publication No. 2002-276637 filed by the present applicant
is suitable to be used as the steel material for high-strength
bolts having excellent fire resistance for realizing the present
invention. As the steel material disclosed in that invention is
characterized by excellent resistance to delayed fracture, and it
has adequate strength at room temperature and also at a high
temperature of 650.degree. C., it is highly suitable to be used as
the material for ultra-high-strength bolts having excellent fire
resistance for realizing the high-strength bolted connection
structure, with no fire protection, of the present invention.
[0083] For example, this steel material may be rolled to a wire rod
and, from the wire rod, high strength bolts having the bolt thread
of, for example, M22 may be formed, and with appropriate quenching
and tempering, the tensile strength of the bolts may be adjusted to
the range of 1200.about.1600 N/mm.sup.2 to obtain the
ultra-high-strength bolts, having excellent fire resistance and
excellent resistance to delayed fracture, to be used in the present
invention. As disclosed in the invention of above-mentioned
Japanese Patent Publication No. 2002-276637, in order to relax the
stress concentration in the bolt thread, it is effective to form
this ultra-high-strength bolts in shape such that bottom shape of
the bolt thread is in the form of arch-like curve.
[0084] The ultra-high-strength bolts having excellent fire
resistance and excellent resistance to delayed fracture used in the
present invention may be applied to all sites. However, as the
required characteristics may differ depending upon the application
site, it is possible to strictly select application sites depending
upon the required characteristics and to thereby reduce the burden
of material cost.
[0085] In the high-strength bolted connection structure of the
present invention, high-temperature strength, especially the level
of the shear proof stress, of the high-strength bolts is required
to be high. However, as the same shear stress as in the
high-strength bolts does not act upon nuts and washers at the time
of a fire when the bolted connection changes into pressure bearing
state, the same high-temperature strength is not required for them
and, therefore, general structural high-strength hexagon nuts and
structural high-strength plain washer having no defined fire
resistance may assure adequate high temperature strength.
[0086] Columns and beam members, or joint metal, used in the
high-strength bolted connection structure to which the present
invention is applied, may be all formed of fire resistant steel
material having adequate high-temperature strength at 600.degree.
C. or higher, for example, NSFR400B, 490B, etc. However, as the
required characteristics may differ depending upon the application
site, it is possible to strictly select application sites for fire
resistant steel material having adequate high-temperature strength
at 600.degree. C. or higher, which imposes large cost burden, and
to thereby reduce the burden of material cost.
[0087] Next, the present invention will be described in detail.
[0088] 1. Case of friction-type high-strength bolted connection
structure
[0089] (1) Example of friction-type high-strength bolted connection
structure
[0090] A friction-type high-strength bolted connection is a
connection method in which joint members are tightly clamped via
high strength bolts so as to transmit stress by the frictional
force produced between members. Representative friction-type
high-strength bolted connection structures include, for example, a
high-strength bolted connection structure as shown in FIG. 1, in
which H-shaped beam members 1a and 1b are joined by high-strength
bolts 3 via outer splice plates 2a and inner splice plates 2b and
side splice plates 2c, or a high-strength bolted connection
structure as shown in FIG. 2, in which brace members 1d and 1e are
joined by high-strength bolts 3 via upper splice plate 2d and lower
splice plate 2e, or a high-strength bolted connection structure as
shown in FIG. 3, in which a beam member 6 is connected to T-shaped
joint metal 7 by high-strength bolts 9. The connection structure
shown in FIG. 3 in which a beam member 6 is connected to T-shaped
joint metal 7 by high-strength bolts 9 and the T-shaped joint metal
7 is connected to a column member 5 by high-strength bolts 8,
includes a friction-type high-strength bolted connection structure
and a tension-type high-strength bolted connection structure, and
the connection structure connecting the T-shaped joint metal 7 to
the column member 5 by the high-strength bolts 8 corresponds to a
tension-type high-strength bolted connection structure to be
described later.
[0091] The present invention is applied, in a first aspect, to the
friction-type high-strength bolted connection structure.
[0092] (2) Concept of verification of fire resistant security of a
friction-type high-strength bolted connection.
[0093] At the time of a high temperature due to fire, in the
friction-type high-strength bolted connection structure in a steel
structure, an introduced axial force is relieved and a sliding load
is lowered due to relaxation of the bolts 3 and beam members (brace
members) and splice plates and a decrease in Young's modulus of
elasticity. However, since it is only required that the
high-strength bolted connection can finally support the long term
load, security of the high-strength bolted connection in fire
resistance design needs only to be evaluated in terms of bearing
proof stress (long term allowable shear proof stress), and not in
terms of sliding proof stress.
[0094] In accordance with equations (2.3), (2.4), Table 2.2, Table
2.3 defined in "Guide for design and work execution of
high-strength bolted connection" published in 1973 and amended in
1993 by Architectural Institute of Japan (corresponding to F10T
(JIS B 1186)), security of the high-strength bolted connection at
the time of fire can be verified if shear proof stress of the bolt
b.tau.t (N/mm.sup.2) at high temperature satisfies the relation
<1>:
b.tau.t.gtoreq..mu..times.N.sub.0/(.nu..times.bAs) <1>
[0095] where
[0096] b.tau.t: shear proof stress of the bolt at high temperature
(N/mm.sup.2)
[0097] b.tau.t=TSt/{square root}3
[0098] TSt: tensile strength of the bolt at high temperature
(N/mm.sup.2)
[0099] .mu.: coefficient of slip at room temperature
[0100] N.sub.0: design bolt tension (N)
[0101] .nu.: safety factor for long term load
[0102] bAs: cross-sectional area of bolt shank (mm.sup.2),
[0103] wherein the design bolt tension (N.sub.0) is expressed, for
example, in accordance with the aforementioned "Guide for design
and work execution of high-strength bolted connection" published by
Architectural Institute of Japan, as follows:
N.sub.0=0.675.times.TS.times.bAe
[0104] where
[0105] TS: tensile strength of the bolt at room temperature
(N/mm.sup.2)
[0106] bAe: effective cross-sectional area of bolt thread
(mm.sup.2).
[0107] For example, when the coefficient of slip (.mu.) is 0.45 and
safety factor for long term load (.nu.) is 1.5, the equation
<1> can be rewritten as equation <1a>:
b.tau.t.gtoreq.0.2025.times.TS.times.(bAe/bAs) <1a>.
[0108] In addition, it can be seen that if, for example, the
tensile strength of the bolt at room temperature (TS) is 1400
N/mm.sup.2 and (the effective cross-sectional area of bolt thread
portion of the bolt/cross-sectional area of bolt shank) (bAe/bAs)
is 0.816 for M16, M20, M24 (JIS B 0123), and 0.832 for M22 (JIS B
0123), the condition that b.tau.t is, from equation <1a>, not
less than 231 N/mm.sup.2 for M16, M20, M24, and not less than 236
N/mm.sup.2 for M22, needs only to be satisfied.
[0109] Further, the present inventors have found that, in the fire
resistant design of a friction-type high-strength bolted connection
structure, since the evaluation is based on long term allowable
shear proof stress, the high-temperature proof stress of nuts and
washers can be finally neglected although it may somewhat affect
the sliding load. Therefore, special fire resistance is not
required to be given to the structural high-strength nuts or
structural high-strength plain washers used in the high-strength
bolted connection of the friction-type connection structure.
[0110] Further, although columns, beams, and joint metal having
assured high-temperature strength are basically used, if a fire
protection is used on a part of columns and beams, columns and
beams may be formed of material of a low high temperature strength
to obtain a connection structure that has substantially no
problem.
[0111] 2. Case of tension-type high-strength bolted connection
structures
[0112] (1) Examples of tension-type high-strength bolted connection
structures
[0113] Tension-type high-strength bolted connection is a connection
method in which stress in axial direction of high-strength bolts is
transmitted, as in friction-type connection, using a compression
force produced between members by tightly clamping the
high-strength bolts. Representative examples of tension-type
high-strength bolted connection structure include, for example, a
connection structure as shown in FIG. 3, FIG. 4(a), and FIG. 4(b),
in which a column 5 and beams 6 (including composite beams) are
connected, via T-shaped joint metal 7, by high-strength bolts 8
(the high-strength bolts connecting the T-shaped joint metal to a
column will be referred to hereinafter as tension bolts 8). As
shown in FIG. 3, FIG. 4(a), and FIG. 4(b), the T-shaped joint metal
and the beam 6 are connected by high-strength bolts 9 in a
friction-type high-strength bolted connection.
[0114] (2) Concept of verification of fire resistant security of a
tension-type high-strength bolted connection.
[0115] In a tension-type high-strength bolted connection, when
heated at the time of fire, thermal expansion of the beam is
constrained by the column so that compression force from the beam
is produced in the tension-type connection. However, as a sliding
load is lowered, a long term load (long term allowable shear force
of the beam) needs to be supported by bearing (shear) of the bolts.
Usually, as shown in FIG. 5, for example, there is a floor slab 10
on the upper flange 6a of the beam 6, and therefore, one may
suppose that the high-strength bolts 8a in the floor slab 10 have
the shear proof stress at room temperature and the remaining
high-strength bolts 8 have the shear proof stress of the bolts at
high temperature. The T-shaped joint metal 7 and the beam 6 are
connected by high-strength bolts 9a in the floor slab 10 on the
upper flange 6a and by the high-strength bolts 9 on lower flange 6b
in a friction-type high-strength bolted connection. Typically,
there are provided studs 11 in the floor slab 10 with the function
of fixing the floor slab 10 to the upper flange 6a of the beam 6
against shearing displacement.
[0116] On the other hand, in a cooling process, after heating, at
the time of fire, shrinkage of the beam 6 is constrained by the
column 5 so that tension from the beam 6 is produced in the
tension-type connection, and therefore, a long term load (long term
allowable shear force of the beam) needs to be supported by bearing
(shear) of bolts. In addition, a tension force due to shrinkage of
the beam 6 acts as an additional axial force so that the
high-strength bolt 8 in the lower flange 6b (and web) of the beam 6
where cooperation of the floor slab cannot be expected, may be
broken. In this situation, one may suppose that the high-strength
bolts 8a in the floor slab 10 on the upper flange 6a of the beam 6
have the shear proof stress at room temperature and remaining
high-strength bolts 8 outside of the floor slab 10 on the upper
flange 6a of the beam 6 have the shear proof stress of the
high-strength bolts at a high temperature.
[0117] From what has been explained above, it can be concluded that
the fire resistant security of tension-type high-strength bolted
connection is determined by the cooling process after heating at
the time of fire wherein the number of bolts that can support the
long term load (long term allowable shear force of the beam) is
less. Therefore, the fire resistant security of a tension-type
connection can be verified by selecting the beam having the long
term allowable shear force Qs (N) at room temperature as an upper
bound such that not only relation <1> is satisfied, but also
following relation <2> between the long term allowable shear
force Qs (N) at room temperature and the shear proof stress at room
temperature b.tau. (N/mm.sup.2) and the shear proof stress at high
temperature b.tau.t (N/mm.sup.2):
Qs.ltoreq.{ns.times.b.tau.+(nf-ns).times.b.tau.t}.times.bAs
<2>
[0118] where
[0119] Qs: long term allowable shear force of the beam at room
temperature (N)
[0120] Qs=fs.times.Ab
[0121] fs: long term allowable shear proof stress of the beam
(N/mm.sup.2)
[0122] Ab: cross-sectional area of the beam (mm.sup.2)
[0123] ns: number of tension bolts in the floor slab on the upper
flange side of the beam
[0124] b.tau.: shear proof stress of bolt at room temperature
(N/mm.sup.2)
[0125] b.tau.=TS/{square root}3
[0126] TS: tensile strength of bolt at room temperature
(N/mm.sup.2)
[0127] nf: number of tension bolts on the upper flange side of the
beam
[0128] b.tau.t: shear proof stress of bolt at high temperature
(N/mm.sup.2)
[0129] b.tau.t=TSt/{square root}3
[0130] TSt: tensile strength of bolt at high temperature
(N/mm.sup.2)
[0131] bAs: cross-sectional area of the bolt shank (mm.sup.2)
[0132] For example, when a tension-type high-strength bolted
connection as shown in FIG. 5 is composed of M22 bolts in the case
of high temperature of 650.degree. C., and shear proof stress of
the bolt at room temperature (b.tau.) is 815 N/mm.sup.2 and shear
proof stress of the bolt at high temperature of 650.degree. C.
(b.tau.t) is 238 N/mm.sup.2, the number of tension bolts 8 on upper
flange 6a of the beam 6 (nf) is 4, for example, and the number of
tension bolts 8a in the floor slab 10 on upper flange 6a of the
beam 6 (ns) is 2, for example, and the cross-sectional area of the
bolt axis (bAs) is 380 mm.sup.2, then it can be seen that the long
term allowable shear force of the beam at room temperature (Qs) can
be selected, from equation <2>, to be 800 kN or lower.
[0133] The present inventors have found that, as a fire resistant
design of the tension-type high-strength bolted connection is
evaluated by shear proof stress of the bolt at room temperature and
at a high temperature, the high-temperature proof stress of nuts
and washers can be neglected. Thus, the structural high-strength
hexagon nuts and the structural high-strength plain washers used as
nuts and washers in the tension-type connection are not required to
be given any special fire resistance.
[0134] Although columns 5, beams 6, and joint metal 7 having
assured high-temperature strength are basically used, if fire
protection is used on a part of columns and beams, columns and
beams formed of material of lower high-temperature strength can be
used to obtain a connection structure that has substantially no
problem.
[0135] 3. Characteristics required for steel for high-strength
bolt
[0136] As regards the steel for high-strength bolts used in the
high-strength bolted connection structure with no fire protection,
that is, friction-type high-strength bolted connection structure
with no fire protection and tension-type high-strength bolted
connection structure with no fire protection of the present
invention, Japanese Patent Publication No. 01-191762 and Japanese
Patent Publication No. 03-173745 disclose a steel material in
which, in view of the fracture surface of bolts due to delayed
fracture indicating grain boundary fracture, impurities such as Mo,
Cr, and the like in the chemical components constituting a steel
are reduced to strengthen the grain boundary, while, in view of
texture control, Mo and Cr are added for high temperature tempering
at 400.degree. C. or higher to give a property such that, even if
hydrogen that is responsible for delayed fracture may enter into
steel, the hydrogen does not readily lead to a fracture. As is
disclosed in Japanese Patent Publication No. 05-9653, reduction of
the impurity P results in reduction of P segregated in the grain
boundary and is particularly effective for strengthening a grain
boundary.
[0137] However, in the case of above-mentioned steel, if hydrogen
enters into steel components in excess of a certain concentration,
a delayed fracture is still induced. Therefore, in order to further
improve the resistance of bolts to delayed fracture, it is
effective to obstruct entrance of hydrogen into steel components,
or to reduce accumulation of hydrogen at prior austenite grain
boundaries.
[0138] As is disclosed in, for example, Japanese Patent Publication
No. 05-70890, a technology for suppressing entrance and diffusion
of hydrogen into steel material by simultaneous addition of Si and
Ni to steel components is proposed. However, such addition of Si
not only impairs a cold forging property of the bolts, but also
leads to an increased cost.
[0139] A steel for bolts is disclosed, in response to the needs as
described above, by the invention in Japanese Patent Publication
No. 07-278735 which, by composite addition of elements Mo, Cr, V
that give rise to notable secondary hardening at the time of
tempering, exhibits tensile strength of 1200 N/mm.sup.2 even when
tempered at high temperature of not lower than 450.degree. C., and
has excellent resistance to delayed fracture. However, even in this
case, there is a problem that, even if tempered at high temperature
of not lower than 450.degree. C., when tensile strength is adjusted
to 1400 N/mm.sup.2 or higher, delayed fracture occurs at higher
rate.
[0140] The present inventors have found, as a result of intensive
study conducted to resolve above-described problem, that an
equation of the relation between the bolt tensile strength and
tempering temperature, and an equation of the relation between the
bolt tensile strength and carbon equivalent calculated from
chemical components of a steel material can be deduced, and have
confirmed that, by selecting the chemical components of a steel so
as to satisfy the two equations, and by suitable quenching and
tempering treatment, a steel material is obtained which can be
heat-treated to give a bolt tensile strength of 1200 N/mm.sup.2 or
higher and has excellent resistance to delayed fracture, and which
is thus highly suitable to be used as a steel material for
high-strength bolts.
[0141] On the other hand, it has been confirmed that the fire
resistant temperature of the steel having Fe as the main component
and containing C, Si, Mn can be improved by adding alloy elements
Cr, Mo, V, for example, used in fire resistant steel, to obtain a
fire resistant temperature level of 600.degree. C. or higher.
[0142] From the foregoing, the present inventors have found that
the high-strength bolt having excellent resistance to delayed
fracture and the high-strength bolt having excellent fire
resistance have a common problem from the viewpoint of chemical
components of steel material so that, by solving this common
problem, an ultra-high-strength bolt can be obtained which has
combined both characteristics and which can realize connection
structure with no fire protection and which has excellent fire
resistance at 650.degree. C.
[0143] (1) Chemical components of steel for ultra-high-strength
bolt
[0144] Examples of chemical components (% by weight) of steel
highly suitable as the steel for ultra-high-strength bolts used in
the high-strength bolted connection structure with no fire
protection, that is, friction-type connection structure with no
fire protection and tension-type connection structure with no fire
protection, of the present invention, will be described below.
[0145] C is an element necessary to assure adequate tensile
strength of steel by a quenching and tempering treatment. If the
content of C is less than 0.30%, adequate strength at room
temperature cannot be assured, and if C is added in excess of
0.45%, the toughness of steel is degraded. Therefore, the content
of C is restricted to the range of not less than 0.30%.about.not
more than 0.45%.
[0146] Si is an element necessary to deoxidize steel and effective
for enhancing strength of steel. If the content of Si is 0.10% or
more, the toughness of steel is degraded and the steel becomes
notably more brittle. Also, as Si is an element which exhibits high
solid solution hardening of ferrite, cold forging is difficult even
when spherodization annealing is performed. In addition, since Si
is an element which is likely to induce grain boundary oxidation at
the time of heat treatment, and resistance to delayed fracture of
bolts tends to be degraded due to its notch effect, the content of
Si should be decreased as far as possible. Therefore, the content
of Si is to be restricted to less than 0.10%.
[0147] Mn is an element that is effective for improving
hardenability. However, if the content is 0.40% or lower, desired
effect cannot be obtained, and if Mn is added in an amount of 1.00%
or more, temper embrittlement is produced, leading to a degradation
of resistance to delayed fracture. Therefore, the content of Mn is
to be restricted to the range of more than 0.40%.about.less than
1.00%.
[0148] P is an element that segregates at the grain boundaries and
lowers the grain boundary strength and degrades resistance to
delayed fracture. P is also an element that, in hydrochloric acid
which is a remarkably corrosive environment, increases the amount
of corrosion of steel through its promoting effect on the hydrogen
production at the steel surface, and therefore, a content of P is
to be lowered as far as possible. If the content of P is 0.010% or
more, amount of hydrogen entering into steel increases notably.
Thus, the content of P is to be restricted to less than 0.010%.
[0149] S is an element that segregates at the grain boundaries and
thereby promotes embrittlement of steel. Therefore, a content of S
is to be lowered as far as possible. If content of S exceeds
0.010%, embrittlement of steel becomes notable. Thus, the content
of S is to be restricted to 0.010% or less.
[0150] Cr is an element that improves hardenability and high
temperature strength of steel and is effective in giving steel the
resistance to temper softening. If the amount of addition is less
than 0.5%, the above-described effect cannot be obtained. Thus, in
view of economy, the added amount is to be restricted to the range
of 0.5% or higher.about.less than 1.5%.
[0151] Mo is an element that is most effective in improving high
temperature strength and is also effective in improving the
resistance to delayed fracture by permitting high temperature
tempering. If the added amount is less than 0.35%, the effect
described above cannot be obtained, and if the added amount is in
excess of 1.5%, a solid solution of undissolved carbide in the
mother phase is unlikely to be produced at the time of tempering,
leading to degradation of ductility. Thus, the added amount is
restricted to the range of more than 0.35%.about.less than
1.5%.
[0152] V is an element that improves strength (including high
temperature strength) of steel by precipitating as minute nitrides
and carbides at the time of tempering, and permits high temperature
tempering, and is also effective in the size reduction of prior
austenite particles. Further, the carbides and nitrides that
precipitate at the time of tempering provide trap sites for
hydrogen and are effective in remarkably improving the resistance
to delayed fracture by decreasing the amount of hydrogen
accumulated at grain boundaries. However, if the added amount is
0.3% or less, particle size No. 10 cannot be achieved for prior
austenite particles, and therefore, the resistance to delayed
fracture cannot be improved. If the added amount exceeds 1.0%, the
cold forging characteristics of bolts are impaired. As V is an
expensive element, economy must also taken into account so that the
content is to be restricted to the range of more than
0.3%.about.1.0% or less.
[0153] (2) Tempering temperature characteristics
[0154] Since delayed fracture occurs as fracture at grain
boundaries of prior austenite grains, in order to improve the
resistance to delayed fracture, it is effective to avoid low
temperature temper embrittlement region of 250.about.400.degree. C.
Further, in order to suppress segregation of film-formed cementite
in prior austenite grain boundaries, it is effective to control the
form of carbides by adopting higher tempering temperature. It is
also effective to precipitate carbides and nitrides of V which
serve as trap sites for hydrogen in order to decrease hydrogen
accumulated in grain boundaries. Thus, it is possible to select a
tempering temperature of 450.degree. C. or higher.
[0155] However, the present inventors were not restricted by the
above-mentioned method, and have found, from experimental results,
that the resistance to delayed fracture can be improved and delayed
fracture can be reliably avoided by selecting tempering temperature
satisfying the equation <3> of the relation between tensile
strength TS (N/mm.sup.2) of high-strength bolts and tempering
temperature (.degree. C.) and the equation <4> of the
relation between tensile strength TS (N/mm.sup.2) of high-strength
bolts and carbon equivalent Ceq (%).
[0156] By using a steel material satisfying these conditions to
form high-strength bolts, ultra-high-strength bolts with tensile
strength (TS) of bolts at room temperature of, for example, 1200
N/mm.sup.2, and having excellent fire resistance with the shear
proof stress (b.tau.t) of bolts at 650.degree. C. satisfying the
above-described relation <1> can be obtained, and by using
these ultra-high-strength bolts, the friction-type high-strength
bolted connection with no fire protection and the tension-type
high-strength bolted connection with no fire protection can be
realized.
TS.ltoreq.(1.1.times.T+850) <3>
TS.ltoreq.(550.times.Ceq+1000) <4>
[0157] where
[0158] TS: tensile strength of high strength bolts at room
temperature (N/mm.sup.2)
[0159] T: tempering temperature (.degree. C.)
[0160] Ceq: carbon equivalent (%)
[0161] Ceq=C+(Mn/6)+(Si/24)+(Ni/40)+(Cr/5)+(Mo/4)+(V/14).
[0162] [Examples of experimental tempering]
[0163] Using the inventive steel samples (1.about.10) having
chemical compositions as shown in Table 1, wire rods of .phi.21.5
mm in diameter were subjected to hot rolling, and high-strength
bolts with bolt thread of M22 were formed and adjusted by quenching
and tempering to tensile strength of bolts in the range of
1200.about.1700 (N/mm.sup.2) to obtain ultra-high-strength
bolts.
[0164] The tensile strength of bolts was adjusted by the
composition of the steel and the tempering temperature, with the
tempering temperature in the range of 290.about.700.degree. C. This
tempering was performed to give high temperature conditions for
evaluating high temperature characteristics. This tempering
temperature T (.degree. C.) and tensile strength TS (N/mm.sup.2) of
ultra-high-strength bolts of experimental examples after tempering
(steel samples 1.about.10) are shown in Table 2 together with the
case of high-strength bolts of comparative examples (steel samples
11.about.18).
[0165] FIGS. 6 and 7 show occurrence or non-occurrence of delayed
fracture after tempering from large specific experimental data
obtained using the inventive steel samples (1.about.10) and
comparative steel samples (11.about.18) shown in Table 1 with
.times. mark (occurrence of delayed fracture) and .largecircle.
mark (no occurrence of delayed fracture) in the Figures. Both
Figures show that delayed fracture did not occur in the region
where above-mentioned relations <3> and <4> are
satisfied.
1TABLE 1 Steel Chemical composition (wt %) sample C Si Mn P S Cr Mo
Al V Ni Ti Nb Ceq 1 0.40 0.07 0.42 0.005 0.009 0.61 1.20 0.020 0.56
0.935 2 0.34 0.04 0.79 0.007 0.003 1.21 0.99 0.015 0.36 0.989 3
0.34 0.03 0.66 0.002 0.002 0.98 0.50 0.062 0.67 0.820 4 0.39 0.07
0.50 0.008 0.008 1.21 0.58 0.025 0.35 0.888 5 0.39 0.05 0.51 0.005
0.009 1.21 0.57 0.021 0.34 0.886 6 0.40 0.08 0.81 0.005 0.008 0.58
0.22 0.019 0.35 0.65 0.04 0.751 7 0.40 0.05 0.54 0.08 0.008 1.00
1.00 0.032 0.32 0.942 8 0.44 0.03 0.85 0.005 0.004 0.90 1.45 0.020
0.70 0.50 0.02 1.188 9 0.43 0.05 0.80 0.005 0.003 1.01 1.20 0.033
0.40 0.20 1.100 10 0.42 0.05 0.75 0.003 0.004 0.83 1.10 0.030 0.40
0.10 0.020 1.020 11 0.41 0.08 0.95 0.007 0.001 1.41 0.93 0.072 0.40
0.00 1.115 12 0.31 0.06 0.50 0.018 0.007 1.01 0.60 0.032 0.29 0.00
0.769 13 0.34 0.17 0.76 0.015 0.017 1.00 0.17 0.025 0.00 0.00 0.716
14 0.19 0.08 0.97 0.013 0.004 0.15 0.00 0.032 0.00 0.00 0.385 15
0.40 0.23 0.81 0.005 0.008 0.58 0.22 0.019 0.00 0.65 0.04 0.732 16
0.32 0.21 0.62 0.010 0.008 1.25 0.59 0.027 0.00 0.00 0.02 0.002
0.830 17 0.30 0.94 0.49 0.011 0.006 1.99 0.20 0.074 0.00 0.00 0.869
18 0.32 0.99 0.46 0.007 0.006 1.97 0.40 0.027 0.00 0.00 0.932 Ceq =
C + (Mn/6) + (Si/24) + (Ni/40) + (Cr/5) + (Mo/4) + (V/14)
[0166]
2 TABLE 2 Tensile Limiting Tempering strength TS .ltoreq. diffusive
Steel temperature TS TS .ltoreq. 550 Ceq + hydrogen sample
(.degree. C.) (N/mm.sup.2) 1.1 T + 850 1000 (ppm) Experimental 1
550 1338 .largecircle. .largecircle. 1.54 examples 2 550 1408
.largecircle. .largecircle. 0.91 3 500 1362 .largecircle.
.largecircle. 1.54 4 625 1426 .largecircle. .largecircle. 1.40 5
650 1312 .largecircle. .largecircle. 1.70 6 450 1316 .largecircle.
.largecircle. 0.70 7 570 1470 .largecircle. .largecircle. 0.90 8
700 1605 .largecircle. .largecircle. 0.95 9 660 1550 .largecircle.
.largecircle. 1.05 10 640 1502 .largecircle. .largecircle. 1.20
Comparative 11 525 1652 X X 0.12 examples 12 440 1469 X X 0.29 13
390 1567 X X 0.05 14 290 1384 X X 0.09 15 435 1482 X X 0.40 16 450
1473 X X 0.45 17 450 1497 X X 0.25 18 400 1651 X X 0.10 Ceq = C +
(Mn/6) + (Si/24) + (Ni/40) + (Cr/5) + (Mo/4) + (V/14) Relation
satisfied: .largecircle. Relation not satisfied: X
EXAMPLE
Example 1
[0167] Example 1 is a case of friction-type high-strength bolted
connection structure in which, as shown in FIG. 1, beams 1a, 1b are
connected via outer splice plate 2a, inner splice plate 2b and side
splice plate 2c by high-strength bolts 3 and in which the beams 1a,
1b, outer splice plate 2a, inner splice plate 2b and side splice
plate 2c are formed of material having assured high-temperature
strength at 650.degree. C.
[0168] FIG. 8 is a view showing, for high-strength bolts with bolt
thread of M22 (JIS B 0123), the relation between shear proof stress
TS/{square root}3 (N/mm.sup.2) of a ultra-high-strength bolts of
the present invention and a test temperature (.degree. C.) together
with the cases of Comparative example 1 (general F10T (JIS B 1186)
bolt), and Comparative example 2 (fire resistant F10T (JIS B 1186)
bolt). The ultra-high-strength bolts of the present invention have
the tensile strength at room temperature adjusted by heat treatment
to 1400 N/mm.sup.2 or higher, and long term allowable shear proof
stress of this ultra-high-strength bolts is 236 N/mm.sup.2. The
long term allowable shear proof stress of Comparative example 1, 2
is 147 N/mm.sup.2.
[0169] FIG. 8 shows that the ultra-high-strength bolts of the
present invention have tensile strength at room temperature of 1412
N/mm.sup.2 (=815 N/mm.sup.2.times.{square root}3), and have the
shear proof stress at 650.degree. C. (b.tau.t) of the bolt
satisfying above-described relation <1> and the shear proof
stress at 650.degree. C. (b.tau.t) is 1.3 times that of Comparative
example 2.
[0170] FIGS. 9, 10, and 11 show, for ultra-high-strength bolts of
the present invention having bolt thread of M16, M20, and M24,
respectively, the relation between the shear proof stress
TS/{square root}3 (N/mm.sup.2) and test temperature (.degree. C.).
Each of the Figures shows that the ultra-high-strength bolts of the
present invention have the shear proof stress of the bolt at
650.degree. C. (b.tau.t) satisfying the relation <1>.
Example 2
[0171] Example 2 is a case of tension-type high-strength bolted
connection structure in which, as shown in FIG. 5, a column 5 and
T-shaped joint metal 7 are connected by high-strength bolts 8 and
there is a floor slab 10. The column 5 and the T-shaped joint metal
are formed of material having assured high temperature strength at
650.degree. C., and the beams are formed of material having tensile
strength in the 400 N/mm.sup.2 class.
[0172] FIGS. 12 and 13 show examples of a tension-type connection
in which a column 5 and a T-shaped joint metal 7 are connected by
high-strength bolts having bolt thread of M22 (JIS B 0123) and
number of tension bolts 8a in the floor slab 10 on upper flange 6a
of the beam 6 are, respectively, two and four.
[0173] Table 3 shows examples of the upper bound of selectable beam
cross section (H-section beam), for the high-strength bolted
connection structure of FIGS. 12 and 13, that is determined from
long term allowable shear proof stress Qs of the beam at
650.degree. C. using the above-described relation <2> based
on numerical values indicated in FIG. 8. From Table 3, it can be
seen that the ultra-high-strength bolts of the present invention
permit a beam having the section H-400.times.200.times.8.times.13
to be selected in the case where number of tension bolts 8a in the
floor slab 10 is two (FIG. 12), and a beam having the section
H-600.times.200.times.12.times.22 to be selected in the case where
number of tension bolts 8a in the floor slab 10 is four (FIG. 13),
and that a beam having larger long term allowable shear proof
stress Qs can be selected than with bolts of the Comparative
examples.
3 TABLE 3 Number of Number of bolts in bolts on floor slab Example
of upper bound of upper on upper Long term selectable beam section
High strength Tension type flange side flange side allowable shear
(for tensile strength of bolt connection of beam: nf of beam: ns
force of beam: Qs 400 N/mm.sup.2 class) Comparative example 1
General F10T 4 2 557 kN or less H-350 .times. 175 .times. 7 .times.
11 bolt 6 4 1,023 kN or less H-600 .times. 200 .times. 9 .times. 12
2 Fire 4 2 620 kN or less H-350 .times. 175 .times. 7 .times. 11
resistant 6 4 1,096 kN or less H-600 .times. 200 .times. 9 .times.
16 F10T bolt Inventive Fire 4 2 800 kN or less H-400 .times. 200
.times. 8 .times. 13 example resistant 6 4 1,420 kN or less H-600
.times. 200 .times. 12 .times. 22 ultra-high strength bolt
[0174] From what has been described in the foregoing, it can be
confirmed that the ultra-high-strength bolts of the present
invention have excellent fire resistance (high temperature
strength) and excellent resistance to delayed fracture at room
temperature and at high temperature of 650.degree. C., and these
characteristics fully satisfy the provisions of "Guide for design
of high strength bolts" published in 1973 and amended in 1993 by
Architectural Institute of Japan, and that, by using these
ultra-high-strength bolts, high-strength bolted connection
structures with no fire protection, that is, friction-type
high-strength bolted connection structures with no fire protection
and tension-type high-strength bolted connection structures with no
fire protection, can be realized.
[0175] The present invention is by no means restricted to
structures and examples as described above, and conditions of the
connection structure and conditions of high-strength bolts
(including fire resistant steel used for construction) may be
modified depending upon the connection to be formed, site of usage,
and environmental conditions, within the scope of the appended
claims.
[0176] The present invention presupposes that, in high-strength
bolted connection structure forming steel structure for which fire
resistance is required, main members to be connected (for example,
columns, beams, or braces) have, basically, an adequate
high-temperature strength at 650.degree. C. and can realize
connection structures with no fire protection, and in order to
fully exploit the high-temperature strength of these main members
(for example, pillars, beams, or braces), the present invention
uses ultra-high-strength bolts having, for example, a 1.4 times or
more larger bolt tensile strength at room temperature than
conventional F10T bolts and a 1.3 times larger shear proof stress
at 650.degree. C. than conventional fire resistive F10T bolts to
realize a high-strength bolted connection structure with no fire
protection at high temperature of 650.degree. C., to thereby
realize reduction of cost as well as reduction of work execution
time.
[0177] For nuts and washers used in the present invention, when the
bolted connection passes to a bearing state at the time of a fire,
the same shear stress as in high strength bolt does not act on nuts
and washers, so that general high-strength hexagon nuts and
structural high-strength plain washers for which no fire resistance
is required may be used to avoid a cost increase.
[0178] Further, a part of beam members and joint metal used in the
present invention can be strictly selected depending upon the site
of usage to thereby reduce the material cost and work execution
time.
* * * * *