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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 displacementsAbstractThis 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 reducedbe
2、am 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 responde
3、d 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 structu
4、ral 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 Earth
5、quake (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 connections unde
6、r 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 the hi
7、ghest 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- rements of
8、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 structu
9、re 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 by an axia
10、l 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 analogous to
11、 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 axial for
12、ces in theFig. 1. Moscone Center Expansion Project in San Francisco, CAgirders result from the accumulated shear in the link.2.Analytical model of CGMRFNonlinear static pushover analysis was conducted on a typical one-bay model of the CGMRF. Fig. 2 shows the dimensions and the various sections of th
13、e 10 in) and the 254 mm (1 1/8 in model. The link flange plates were 28.5 mm 18 3/4 in). The SAP 2000 computer 476 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 1170 which n
14、o 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 yield stress
15、 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 was calcu- l
16、ated 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, Item a. A strai
17、n 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 yield strength o
18、f 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 moment, shear forc
19、e, 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 in Fig. 5 is fun
20、damentally 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 pushover analysis
21、was carried out by applying monotonicallyincreasing 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 mechanism for the
22、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 the beam plastic
23、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 outlined in Section 9
24、 (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 expected yield strength
25、s (Grade 50 steel, Fy=345 MPa and Ry =1.1 are used). 3. Experimental programThe 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 geometry, it follow
26、s 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 behavior of a typical
27、 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 twenty-four 32 mm diame
28、ter 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 exceed , therefore Paxial i
29、s 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 actuators pull the specimen,
30、 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
31、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.The member sizes and the results of tensile coupon tests are listed in Table 2All of the columns and beams were of A572 Grade 50 steel (Fy 344.5
32、MPa). The actual measured beam flange yield stress value was equal to 372 MPa (54 ksi), while the ultimate strength ranged from 502 MPa (72.8 ksi) to 543 MPa (78.7 ksi).Table 3 shows the values of the plastic moment for each specimen (based on measured tensile coupon data) at the full cross-section
33、and at the reduced section at mid-length of the RBS cutout.The specimens were designated as specimen 1 through specimen 4. Test specimens details are shown in Fig. 9 through Fig. 12. The following features were utilized in the design of the beamcolumn connection:The use of RBS in beam flanges. A cir
34、cular cutout was provided, as illustr- ated in Figs. 11 and 12. For all specimens, 30% of the beam flange width was removed. The cuts were made carefully, and then ground smooth in a direct- tion parallel to the beam flange to minimize notches.Use of a fully welded web connection. The connection bet
35、ween the beam web and the column flange was made with a complete joint penetration groove weld (CJP). All CJP welds were performed according to AWS D1.1 Structural Welding CodeUse of two side plates welded with CJP to exterior sides of top and bottom beam flan- ges, from the face of the column flang
36、e to the beginning of the RBS, as shown in Figs. 11 and 12. The end of the side plate was smoothed to meet the beginning of the RBS. The side plates were welded with CJP with the column flanges. The side plate was added to increase the flexural capacity at the joint location, while the smooth transi
37、tion was to reduce the stress raisers, which may initiate fractureTwo longitudinal stiffeners, 95 mm 35 mm (3 3/4 in 1 3/8 in), were welded with 12.7 mm (1/2 in) fillet weld at the middle height of the web as shown in Figs. 9 and 10. The stiffeners were welded with CJP to column flanges.Removal of w
38、eld tabs at both the top and bottom beam flange groove welds. The weld tabs were removed to eliminate any potential notches introduced by the tabs or by weld discontinuities in the groove weld run out regionsUse of continuity plates with a thickness approximately equal to the beam flange thickness.
39、One-inch thick continuity plates were used for all specimens.While the RBS is the most distinguishing feature of these test specimens, the longitudinal stiffener played an important role in delaying the formation of web local buckling and developing reliable connection4. Loading history Specimens we
40、re tested by applying cycles of alternated load with tip displacement increments of _y as shown in Table 4. The tip displacement of the beam was imposed by servo-controlled actuators 3 and 4. When the axial force was to be applied, actuators 1 and 2 were activated such that its force simulates the s
41、hear force in the link to be transferred to the beam. 0.5_y. After+The variable axial force was increased up to 2800 kN (630 kip) at that, this lo- ad was maintained constant through the maximum lateral displacement. maximum lateral displacement. As the specimen was pushed back the axial force remai
42、ned constant until 0.5 y and then started to decrease to zero as the specimen passed through the neutral position 4. According to the upper bound for beam axial force as discussed in Section 2 of this paper, it was concluded that P =2800 kN (630 kip) is appropriate to investigate this case in RBS lo
43、ading. The tests were continued until failure of the specimen, or until limitations of the test set-up were reached.5. Test resultsThe hysteretic response of each specimen is shown in Fig. 13 and Fig. 16. These plots show beam moment versus plastic rotation. The beam moment is measured at the middle
44、 of the RBS, and was computed by taking an equiva- lent beam-tip force multiplied by the distance between the centerline of the lateral actuator to the middle of the RBS (1792 mm for specimens 1 and 2, 3972 mm for specimens 3 and 4). The equivalent lateral force accounts for the additional moment du
45、e to P effect. The rotation angle was defined as the lateral displacement of the actuator divided by the length between the centerline of the lateral actuator to the mid length of the RBS. The plastic rotation was computed as follows 4:where V is the shear force, Ke is the ratio of V/q in the elasti
46、c range. Measurements and observations made during the tests indicated that all of the plastic rotation in specimen 1 to specimen 4 was developed within the beam. The connection panel zone and the column remained elastic as intended by design.5.1. Specimens 1 and 2The responses of specimens 1 and 2
47、are shown in Fig. 13. Initial yielding occurred during cycles 7 and 8 at 1_y with yielding observed in the bottom flange. For all test specimens, initial yielding was observed at this location and attributed to the moment at the base of the specimen 4. Progressing through the loading history, yieldi
48、ng started to propagate along the RBS bottom flange. During cycle 3.5_y initiation of web buckling was noted adjacent to the yielded bottom flange. Yielding started to propagate along the top flange of the RBS and some minor yielding along the middle stiffener. During the cycle of 5_y with the incre
49、ased axial compression load to 3115 KN (700 kips) a severe web buckle developed along with flange local buckling. The flange and the web local buckling became more pronounced with each successive loading cycle. It should be noted here that the bottom flange and web local buckling was not accompanied by a significant deterioration in