1、 土木工程建筑外文文献及翻译 Cyclic behavior of steel moment frame connections under varying axial load and lateral displacements Abstract This paper discusses the cyclic behavior of four steel moment connections tested under variable axial load and lateral displacements. The beam specim- ens consisted of a reduc
2、edbeam section, wing plates and longitudinal stiffeners. The test specimens were subjected to varying axial forces and lateral displace- ments to simulate the effects on beams in a Coupled-Girder Moment-Resisting Framing system under lateral loading. The test results showed that the specim- ens resp
3、onded in a ductile manner since the plastic rotations exceeded 0.03 rad without significant drop in the lateral capacity. The presence of the longitudin- al stiffener assisted in transferring the axial forces and delayed the formation of web local buckling. 1. Introduction Aimed at evaluating the st
4、ructural performance of reduced-beam section (RBS) connections under alternated axial loading and lateral displacement, four full-scale specimens were tested. These tests were intended to assess the performance of the moment connection design for the Moscone Center Exp- ansion under the Design Basis
5、 Earthquake (DBE) and the Maximum Considered Earthquake (MCE). Previous research conducted on RBS moment connections 1,2 showed that connections with RBS profiles can achieve rotations in excess of 0.03 rad. However, doubts have been cast on the quality of the seismic performance of these connection
6、s under combined axial and lateral loading. The Moscone Center Expansion is a three-story, 71,814 m2 (773,000 ft2) structure with steel moment frames as its primary lateral force-resisting system. A three dimensional perspective illustration is shown in Fig. 1. The overall height of the building, at
7、 the highest point of the exhibition roof, is approxima- tely 35.36 m (116ft) above ground level. The ceiling height at the exhibition hall is 8.23 m (27 ft) , and the typical floor-to-floor height in the building is 11.43 m (37.5 ft). The building was designed as type I according to the requi- reme
8、nts of the 1997 Uniform Building Code. The framing system consists of four moment frames in the EastWest direct- ion, one on either side of the stair towers, and four frames in the NorthSouth direction, one on either side of the stair and elevator cores in the east end and two at the west end of the
9、 structure 4. Because of the story height, the con- cept of the Coupled-Girder Moment-Resisting Framing System (CGMRFS) was utilized. By coupling the girders, the lateral load-resisting behavior of the moment framing system changes to one where structural overturning moments are resisted partially b
10、y an axial compressiontension couple across the girder system, rather than only by the individual flexural action of the girders. As a result, a stiffer lateral load resisting system is achieved. The vertical element that connects the girders is referred to as a coupling link. Coupling links are ana
11、logous to and serve the same structural role as link beams in eccentrically braced frames. Coupling links are generally quite short, having a large shear- to-moment ratio. Under earthquake-type loading, the CGMRFS subjects its girders to wariab- ble axial forces in addition to their end moments. The
12、 axial forces in the Fig. 1. Moscone Center Expansion Project in San Francisco, CA girders result from the accumulated shear in the link. 2. Analytical model of CGMRF Nonlinear static pushover analysis was conducted on a typical one-bay model of the CGMRF. Fig. 2 shows the dimensions and the various
13、 sections of the 10 in) and the254 mm (1 1/8 in model. The link flange plates were 28.5 mm 18 3/4 in). The SAP 2000 computer476 mm (3 /8 in web plate was 9.5 mm program was utilized in the pushover analysis 5. The frame was characterized as fully restrained(FR). FR moment frames are those frames for
14、 1170 which no more than 5% of the lateral deflections arise from connection deformation 6. The 5% value refers only to deflection due to beamcolumn deformation and not to frame deflections that result from column panel zone deformation 6, 9. The analysis was performed using an expected value of the
15、 yield stress and ultimate strength. These values were equal to 372 MPa (54 ksi) and 518 MPa (75 ksi), respectively. The plastic hinges loaddeformation behavior was approximated by the generalized curve suggested by NEHRP Guidelines for the Seismic Rehabilitation of Buildings 6 as shown in Fig. 3. y
16、 was calcu- lated based on Eqs. (5.1) and (5.2) from 6, as follows: PM hinge loaddeformation model points C, D and E are based on Table 5.4 from 6 for y was taken as 0.01 rad per Note 3 in 6, Table 5.8. Shear hinge load- loaddeformation model points C, D and E are based on Table 5.8 6, Link Beam, It
17、em a. A strain hardening slope between points B and C of 3% of the elastic slope was assumed for both models. The following relationship was used to account for momentaxial load interaction 6: where MCE is the expected moment strength, ZRBS is the RBS plastic section modulus (in3), is the expected y
18、ield strength of the material (ksi), P is the axial force in the girder (kips) and is the expected axial yield force of the RBS, equal to (kips). The ultimate flexural capacities of the beam and the link of the model are shown in Table 1. Fig. 4 shows qualitatively the distribution of the bending mo
19、ment, shear force, and axial force in the CGMRF under lateral load. The shear and axial force in the beams are less significant to the response of the beams as compared with the bending moment, although they must be considered in design. The qualita- tive distribution of internal forces illustrated
20、in Fig. 5 is fundamentally the same for both elastic and inelastic ranges of behavior. The specific values of the internal forces will change as elements of the frame yield and internal for- ces are redistributed. The basic patterns illustrated in Fig. 5, however, remain the same. Inelastic static p
21、ushover analysis was carried out by applying monotonically increasing lateral displacements, at the top of both columns, as shown in Fig. 6. After the four RBS have yielded simultaneously, a uniform yielding in the web and at the ends of the flanges of the vertical link will form. This is the yield
22、mechanism for the frame , with plastic hinges also forming at the base of the columns if they are fixed. The base shear versus drift angle of the model is shown in Fig. 7 . The sequence of inelastic activity in the frame is shown on the figure. An elastic component, a long transition (consequence of
23、 the beam plastic hinges being formed simultaneously) and a narrow yield plateau characterize the pushover curve. The plastic rotation capacity, qp, is defined as the total plastic rotation beyond which the connection strength starts to degrade below 80% 7. This definition is different from that out
24、lined in Section 9 (Appendix S) of the AISC Seismic Provisions 8, 10. Using Eq. (2) derived by Uang and Fan 7, an estimate of the RBS plastic rotation capacity was found to be 0.037 rad: Fyf was substituted for RyFy 8, where Ry is used to account for the differ- ence between the nominal and the expe
25、cted yield strengths (Grade 50 steel, Fy=345 MPa and Ry =1.1 are used). 3. Experimental program The experimental set-up for studying the behavior of a connection was based on Fig. 6(a). Using the plastic displacement dp, plastic rotation gp, and plastic story drift angle qp shown in the figure, from
26、 geometry, it follows that: And: in which d and g include the elastic components. Approximations as above are used for large inelastic beam deformations. The diagram in Fig. 6(a) suggest that a sub assemblage with displacements controlled in the manner shown in Fig. 6(b) can represent the inelastic
27、behavior of a typical beam in a CGMRF. The test set-up shown in Fig. 8 was constructed to develop the mechanism shown in Fig. 6(a) and (b). The axial actuators were attached to three 2438 mm 1219 mm 1219 mm (8 ft 4 ft 4 ft) RC blocks. These blocks were tensioned to the laboratory floor by means of t
28、wenty-four 32 mm diameter dywidag rods. This arrangement permitted replacement of the specimen after each test. Therefore, the force applied by the axial actuator, P, can be resolved into two or thogonal components, Paxial and Plateral. Since the inclination angle of the axial actuator does not exce
29、ed , therefore Paxial is approximately equal to P 4. However, the lateral3.0 component, Plateral, causes an additional moment at the beam-to column joint. If the axial actuators compress the specimen, then the lateral components will be adding to the lateral actuator forces, while if the axial actua
30、tors pull the specimen, the Plateral will be an opposing force to the lateral actuators. When the axial actuators undergo axial actuators undergo a lateral displacement _, they cause an additional moment at the beam-to-column joint (P- effect). Therefore, the moment at the beam-to column joint is equal to: where H is the lateral forces, L is the arm, P is the axial force and _ is the lateral displacement. Four full-scale experiments of beam column connections were conducted.
