《AISC kulak1990Q2.pdf》由会员分享，可在线阅读，更多相关《AISC kulak1990Q2.pdf（8页珍藏版）》请在三一文库上搜索。
1、Design of Connectors in Web-Flange Beam or Girder Splices GEOFFREY L. KULAK and DEBORAH L. GREEN INTRODUCTION Splices in beams and girders are often required when the lengths of members are limited by fabrication, transportation, or handling facilities available, or by the construction process. A co
2、mmonly used bolted splice is shown in Fig. 1. Splice plates are lapped across the joint and bolted to the webs and the flanges of the beam in order to transfer the load. This type of splice is usually referred to as a web- flange splice. Current design methods for the connectors in web-flange splice
3、s vary. For example, Fisher and Struik 1 recommend that the web splice be assumed to transfer all of the shear and that the flange splice be assumed to transfer all of the moment at the section. The bolt group on one side of the web splice is designed on the assumption that the shear force acts at t
4、he centroid of the bolt group on the opposite side of the splice. In a commonly used British design manual, 2 the same approach is recommended. Ballio and Mazzolani 3 present two alternative approaches for design of web-flange splices. In both approaches, the moment at the location of the splice is
5、proportioned between the web splice and the flange splice. For the web splice, the first approach considers the shear force to act at the centroid of the opposite bolt group. This is similar to the recommendation of Fisher and Struik. In the second approach, the bolt group on one side of the web spl
6、ice is designed assuming that the shear force acts at the centerline of the splice. Bresler, Lin and Scalzi, 4 Salmon and Johnson,5 and Nethercot 6 also use this second approach, and they further recommend that the web splice be designed to transmit both the eccentric shear force and the portion of
7、the moment that the web was designed to carry. However, Salmon and Johnson suggest that the effect of the eccentricity can be neglected except in cases where the shear and moment are high, and Bresler, et al. recommend neglecting the effect of the eccentricity when the eccentricity is much less than
8、 the depth of the web. The validity of these web-flange splice design assumptions has not been substantiated on an analytical basis. Furthermore, very little experimental work has been Geoffrey L. Kulak is professor of civil engineering, University of Alberta, Edmonton, Canada. Deborah L. Green is w
9、ith Eastern Designers, Fredericton, NB, Canada, formerly a graduate student, Department of Civil Engineering, University of Alberta, Edmonton, Canada. carried out to verify any of the design approaches. As far as can be established, the work of Garrelts and Madsen in 1941 is the only experimental st
10、udy that has been carried out to investigate the behaviour of riveted or bolted web-flange girder splices. 7 However, their data do not verify the exact distribution of the force in a web splice. The current AISC specifications 8,9 require that bolted beam or girder splices resist the most unfavorab
11、le combination of shear and moment at the location of the splice. However, they do not provide insight into how the eccentric effect of the shear force should be accounted for in the design of a web splice or how the moment at the section should be proportioned between the web splice and the flange
12、splices. This paper is a summary of the results of a study carried out to establish a rational design procedure for the connectors in a bolted web-flange beam or girder splice in which both the web and the flange material are spliced at the same location. ANALYTICAL STUDY A theoretical approach to p
13、redict the ultimate capacity of a web-flange beam or girder splice has recently been proposed by Kulak, et al. 10 It is a development similar to the method currently used to determine the ultimate strength of eccentrically loaded bolted connections, 8,9 that is, it is a rational approach that satisf
14、ies the equations of static equilibrium and uses the true shear load versus shear deformation response of the fasteners. Figure 2(a) shows a simple beam that contains a bolted web-flange splice located in a region where both shear and moment are present. A free-body diagram taken by cutting the beam
15、 through one set of fasteners is shown in Fig. 2(b). The forces in these fasteners are assumed to rotate about an Fig. 1. Bolted web-flange girder splice SECOND QUARTER / 199041 instantaneous center, as shown in this figure. The location of the instantaneous center of rotation is identified 10 when
16、the three equations of equilibrium are satisfied, namely: Fx = 0(1) Fy = 0(2) M = 0(3) Equation 1 is automatically satisfied because there are no external horizontal forces present. Equation 2 is satisfied when the sum of the vertical components of the bolt forces is equal to the shear acting at the
17、 section. For the member shown in Fig. 2, the result of taking the sum of the vertical forces to equal zero is: Pb L n iI Riv = = 0(4) The result of taking the sum of the moments about the (a) (b) Fig. 2. Analytical model for a web-flange splice. instantaneous center to equal zero is: Pb L xxrF d n
18、i R r oofi i ()+ = = 1 0(5) Equation 5 can be rewritten as: Pbx L Pb L xrF d n i R r ooji i + = =() 1 0(6) where d= distance between the centroids of the top and bottom flange splice plates Ff= force in the top or bottom flange bolts on one side of the splice n = number of bolts on one side of the w
19、eb splice ri = distance from the ith bolt to the instantaneous center of rotation ro= distance from the centroid of one bolt group to its instantaneous center of rotation Ri= force in the ith bolt Riv= vertical component of the bolt force Ri xo= distance from the centerline of the splice to the cent
20、roid of the bolt group on one side of the splice. Although this development started with a single concentrated load acting on a simply supported beam, it can be shown that the foregoing statements are true for any general loading case. Therefore, in order to present these equations in a general form
21、, Pb/L will be replaced by V, the shear at the section, and Pbx/L will be replaced by M, the moment at the centerline of the splice. Using this notation, the equilibrium equations become: n i RV iv = = 1 0(7) n i R rF dMV xr i ifoo = += 1 0()(8) Equation 7 identifies that it is the vertical componen
22、ts of the bolt forces that resist the transverse shear at the section. Equation 8 identifies how the moment transferred across the splice is shared between the bolts in the web splice and the bolts in the flange splices. Althought Kulak, et al. recognized that it would be advantageous from a designe
23、rs point of view if a location of the eccentric shear force could be established that would yield results identical to those given by the equilibrium equations, they found no particular relationship between the eccentricity of the shear force and the center of gravity of either bolt group. However,
24、a further examination of the equilibrium equations shows that the term V(xo + ro) is the moment at the instantaneous center produced by the eccentric shear force. This leads to a solution to the problem which is 42ENGINEERING JOURNAL / AMERICAN INSTITUTE OF STEEL CONSTRUCTION identical to that for a
25、 bolt group loaded eccentrically by a force V located at a distance xo from its center of gravity. In other words, for a web splice located at a point of contraflexure, the design of the bolt group on the one side of the splice can proceed on the same basis as that for a bolt group acting under a lo
26、ad equal to the shear at the splice and located at the centerline of the splice. Design aids are available for this case. In allowable stress design, the procedures and design aids presented in the 9th edition of the AISC Manual can be used; 8 if load and resistance factor design is the basis of the
27、 design, then the 1st edition of the LRFD Manual should be used. 9 A small problem in nomenclature arises. The distance between the shear force and the centroid of the bolt group, called xo in the development so far, is given different symbols in the two AISC manuals, and is referred to by yet other
28、 different symbols in other design aids. 11 However, most general references and textbooks 1,5,10 refer to this distance as the eccentricity e. In order to avoid confusion, that symbol will be adopted here. Therefore, Eq. 8 will be rewritten as n i R rF dMV er i ifo = += 1 0()(9) Equations 7 and 9 a
29、re general and can be applied to bolted web-flange splices in both simple and continuous beams. For the special case of a beam in which only the web is spliced, but wherein both shear and moment are present, there are no forces transferred across the flanges. The equilibrium equations yield results
30、identical to designing the bolt group on one side of the splice to resist the shear and moment at the centerline of the splice, applied to the bolt group as shown in Fig. 3. The ultimate capacity of the bolt group can then be determined using the ultimate strength method for analyzing eccentrically
31、loaded connections. For the case of a beam or girder in which both the web and the flanges are spliced, the designer will have to make an assumption regarding the portion of the moment at the location of the splice that the flange splices will be designed to resist. This assumption is then used in E
32、q. 9 to identify how the moment is shared between the web splice and the flange splices. Traditionally, the flange splices have been designed to resist either 100 percent of the moment at the centerline of the splice or the portion of the moment that the flanges in the beam or girder were designed t
33、o resist. Either one of these approaches may be used as long as the equilibrium statements (Eqs. 7 and 9) are satisfied. (If the designer chooses to provide a flange splice connecton that is based on the assumption that the flanges carry 100 percent of the moment, then obviously the flange splice is
34、 designed conservatively. The concomitant question is whether the web splice at the same location designed only for shear, that is, neglecting the proportion of the total moment that must be present in the web, will be satisfactory. There have not been any physical tests covering this case. However,
35、 design procedures for the beam itself include the assumption that an I-shaped cross section can attain the full plastic moment capacity even though the web is fully yielded in shear. 12 This is the result of the beneficial effect of strain-hardening of the flange material: the flanges pick up the r
36、elatively small contribution that the web makes to the total moment capacity. In the web and flange splice case, the flange splice plates should behave similarly to the flanges of any unspliced beam, that is, the flanges should be capable of carrying all of the moment. As far as the web bolts themse
37、lves are concerned, the rigid body movement of the beam relative to the splice means that the deformation imposed on any of the bolts due to moment will always be a maximum in the flange splice bolts. Thus, assigning all the moment to the flange splice plates and all the shear to the web splice plat
38、es should be a satisfactory situation.) In order to substantiate the analytical procedure just presented, an experimemtal program was established. Tests of large-size spliced members were carried out in order to establish the ultimate capacity of bolted web splices in which the number and arrangemen
39、t of bolts varied. The experimental results were compared with analytical predictions. The web splice design approach which uses the assumption that the shear force acts at the centerline of the splice will subsequently be referred to as the “proposed method of analysis.“ The web splice design appro
40、ach which uses the assumption that the shear force acts at the centroid of the opposite bolt group will subsequently be referred to as the “conventional method of analysis.“ EXPERIMENTAL PROGRAM In order to be able to predict the capacity of a group of Fig. 3. Web splice bolt group design forces. SE
41、COND QUARTER / 199043 fasteners in the full-size test specimens, it is necessary first to know the load versus deformation response of a typical individual fastener. In this program, both a tension jig and a compression jig 10 were used, although, as will be noted subsequently, the tension test jig
42、results are considered to more closely represent actual conditions. The specimens were detailed to conform as closely as possible to the details in each of the full-scale test configurations. In all cases, the steel plates used to make the jig were cut from the same material that was used to fabrica
43、te the full-size bolted web splice test specimens described subsequently. The test bolts were in. diameter ASTM A325 bolts, 3 in. in length, of which 1 3 8 in. was threaded. Any possible variation in the bolt properties was minimized by using bolts that were all from the same production lot. The bol
44、ts were tightened to the snug position. The large-scale web splice test specimens were constructed by joining two steel beams together using two steel splice plates, one on either side of the web. These plates were lapped across the joint and bolted to the beam webs. The dimensions of the beams were
45、 chosen so that the beams would not yield before the bolt group in the web splice reached its ultimate capacity. The steel in the beams was required to meet CSA Specification G40.21-M 300W. The specified minimum yield strength of this steel is 300 MPa, 13 or about 44 ksi. Six different splices were
46、tested. In all cases, the thickness of the beam webs was in. The thickness of the splice plates used in specimens C1 through C4 (see Table 1) was also in. These splice plates were cut from the same plate that was used to make the beam webs. The thickness of the splice plates used in the remaining tw
47、o specimens, C5 and C6, and was in. The other dimensions of the splice plates were simply a reflection of the bolt patterns used. Details of the geometry of the bolted web splices are provided in Table 1. In all of the full-scale tests, the connections used in in. diameter ASTM A325 bolts from the s
48、ame lot as those used in the single bolt shear specimens. A in. drill bit was used to ensure that all of the bolts would be bearing against the web and the splice plates as soon as a load was applied. The initial slippage was minimized by the small clearance of the bolt holes. Although this represen
49、ts an idealized condition, it prevents another variable (slippage) from being introduced into the experiment. It is felt that the idealized condition approximates the behavior of the bolts in a real connection as the connection reaches its ultimate capacity. The bolts were tightened to the snug condition. The set-up used to test the bolted web splice specimens is shown in Fig. 4. Two independently controlled hydraulic jacks were used to apply vertical loads to the specimen, and the loads applied to the specimen were measured using electronic load