FOUR-PLATE HEB-100 BEAM SPLICE BOLTED CONNECTIONS: TESTS AND COMMENTS

Transcription

1 FOUR-PLATE HEB- BEAM SPLICE BOLTED CONNECTIONS: TESTS AND COMMENTS M.D. Zygomalas and C.C. Baniotopoulos Institute of Steel Structures, Aristotle University of Thessaloniki, Greece ABSTRACT The present research work concerns the laboratory testing of a full strength bolted splice connection for a HEB profile. Taking as reference results those obtained from a continuous intact beam subjected to a concentrated force at the middle of its span, eight simply supported beams with full strength bolted splice connections have been tested. The obtained test results significantly diverge from the reference ones obtained from the intact beam. INTRODUCTION The use of non-pretensioned bolts in full strength splice connections is a coon practice in several countries (1)(2). However, in such splices first due to the difference between the diameter of bolts and the respective holes and second due to a possible preliminary imperfection (rotation of the connected parts of the beam), an additional significant deflection is caused as soon as the loading is applied on the beam and before its value reaches the calculated value. Scope of the present research work was to experimentally define the relationship between the moment at the middle of the span and the deflection at the same point. As a matter of fact, the latter is tightly connected to the Serviceability Limit State of the beam, even before the total loading at the middle of the span has been applied (3). For the laboratory tests, HEB-beams have been selected because the chosen profile is very often used as a structural member in a plethora of steel structures (cf. e.g. the purlins of steel roofs). The material used was Fe 36 and the non-pretensioned bolts were M and M Four groups of different connections were used, once with bolts M12 and once with bolts M14. Two steel plates having cross section 6x8 were used to connect the webs, whereas another two with cross section 12x to connect the flanges. The full strength bolted splices have been designed and constructed so that they exhibit at least the same load-bearing capacity as the intact beam (4). CALCULATION OF THE CONNECTIONS The maximum moment and shear force that the selected profile HEB can carry under the plastic limits of strength are equal to: M pl.y.rd = W pl.y * f y /γ M = 14,2 * 23,5/1,1 = 2221,818 cm and Connections in Steel Structures V - Amsterdam - June 3-4, 4 287

2 V pl.y.rd = 1,4 * h * t w * f y /(3 ½ * γ M ) = 1,4*1*,6*23,5 /( 3 ½ * 1,1) = 76,966 For the connection of the two separated parts of the beam, two horizontal steel plates with cross section 1*1,2 cm were used for the flanges and two vertical ones with a cross section,6*5,5 cm for the web (cf. e.g. Figure 1). CALCULATION OF THE ADDITIONAL PARTS OF THE WEBS Figure 1. The splice connection (left) and the vertical additional plate (right). The additional horizontal plates on the flanges were used to transfer the moment in the connection area, whereas the additional vertical ones were used to carry the shear forces. Because of the syetry of beam and loading, only half of a vertical plate was drawn and calculated. In Figure 1 a half of one of the two additional vertical plates is shown where the geometrical position of the center of the holes is the point of the load application. Note that in such splices the shear forces are not the principal problem. The same position and the same kind of bolts were used for all specimens. The experimental results showed that these vertical additional parts of the connection did not take or carry any force during the experiment. In the following equations, calculations and symbols from EC3 were used (4). A 6 bolt connection was used for M bolts for the half of the connection of a flange. The position of the bolts is shown in Figure 1. The horizontal distance between the two connected pieces of the beam was equal to 1,5 cm for all the specimens. P y =79,966/2=38,48 M=9*P y =348,347 cm P y : (V x,.p = V y,.p =Py/3=12,828) I p =Σ(xi 2 +yi 2 )=2*5 2 = M (V y,m =M*x i /I p =346,347*5/=34,635 V x,m =My i /I p = ) V x = V y =12,828+34,635=47,463 t=min(t κ Λ =,6 s/2=,6/2=,3) t=,3 α=min(e 1 /(3*1,5)=4/4,5=,889 p 1 /(3*1,5)-1/4=,861 8/36=2,2 1) α=,861 F v.rd =,6*f ub *A/γ Mb =,6*8*1,54/1,25=59,136 KN > 47,463 F b,rd =2,5*α*f u *d*t/γ Mb =2,5*,861*8*1,4*,3/1,254=57,859 > 47, Connections in Steel Structures V - Amsterdam - June 3-4, 4

3 The cross section of,5*5,5 cm was not available in the market and for this reason, a crosssection,6*8 cm was used for the splice under investigation. CALCULATION OF THE ADDITIONAL PARTS OF THE FLANGES Two groups of four different positioning of the bolts were used for the specimens. For the first group, bolts type M were used calculated for the connections on the flanges. For the second group, bolts type M were used in an effort to optimize the deformation of the connected areas. Calculations were not repeated because the change in the diameter of the bolts was in the safe side. SPECIMENS B1 AND B2 The suggested position of the bolts is shown in Figure 2 (diameters for the holes d o =13 and d o =15 ) corresponding to specimens B1 and B2. Figure 2. The position of the holes in the additional horizontal splice plates and flanges (specimens B1 and B2). Calculation of the strength of the connection d o = 13 A=11,3 f ub = 8 /cm 2 f yb =64 /cm 2 t = min ( t=1 t Λ π =1,2) t = 1 cm α = min ( 4/(3*1,3)=1,26 8/(3*1,3)-1/4=1,8 8/36=2,22 1) α=1 F sd = M sd /z = 22,218/(1+,6+,6)*1-2 = 198,375 F v.rd =,6*f ub *A/γ Mb =,6*8*1,13/1,25=43,392 > 198,375/5=39,675 F b.rd =2,5*α*f u *d*t/γ Mb =2,5*1*8*1,2*1/1,25=192 > 39,675 SPECIMENS B3 AND B4 In an effort to add more stiffness to the area of the connection in order to obtain better results during deformation, it was decided that the distance between the holes to be greater in the specimens B3 and B4 than the distance in the specimens B1 and B2. The positions of the bolts in specimens B3 and B4 is shown in Figure 3. Connections in Steel Structures V - Amsterdam - June 3-4, 4 289

4 Figure 3. The position of the holes in the additional splice plates and the flanges (specimens B3, B4). Calculation of the strength of the connection Similarly to the calculation for specimens B1, B2, the present one leads to safe results. SPECIMENS B5 AND B6 Figure 4. The position of the holes in the additional splice plates and the flanges (specimens B5 and B6). Calculation of the strength of the connection d o = 13 A=11,3 f ub = 8 /cm 2 f yb =64 /cm 2 t = min ( t=1 t Λ π =1,2) t = 1 cm α = min ( 4/(3*1,3)=1,26 4/(3*1,3)-1/4=,776 8/36=2,22 1) α=,776 F sd = M sd /z = 22,218/(1+,6+,6)*1-2 = 198,375 F v.rd =,6*f ub *A/γ Mb =,6*8*1,13/1,25=43,392 > 198,375/6=33,67 F b.rd =2,5*α*f u *d*t/γ Mb =2,5*,776*8*1,2*1/1,25=148,992 > 33,67 29 Connections in Steel Structures V - Amsterdam - June 3-4, 4

5 SPECIMENS B7 AND B8 Figure 5. The position of the holes in the additional splice plates and the flanges for specimens B7, B8. Calculation of the strength of the connection d o = 13 A=11,3 f ub = 8 /cm 2 f yb =64 /cm 2 t = min ( t=1 t π Λ =1,2) t = 1 cm α = min ( 3/(3*1,3)=,769 3/(3*1,3)-1/4=,776 8/36=2,22 1) α=,519 F sd = M sd /z = 22,218/(1+,6+,6)*1-2 = 198,375 F v.rd =,6*f ub *A/γ Mb =,6*8*1,13/1,25=43,392 > 198,375/6=33,67 F b.rd =2,5*α*f u *d*t/γ Mb =2,5*,519*8*1,2*1/1,25=99,648 > 33,67 SPECIMEN (REFERENCE) This specimen was used as an intact beam without any kind of splice connection. The respective test results were used as reference for the rest experimental results of the specimens B1 - B8. EXPERIMENTS AND TEST RESULTS All the experiments were performed at the Laboratory of the Institute of Steel Structures, Department of Civil Engineering, Aristotle University of Thessaloniki, Greece. All the specimens used were simply supported beams with a span of 1 meter and a concentrated vertical force in the middle of their span. A composite hydraulic machine was used with an upper limit of force equal to. A computer was used to record and store pairs of values corresponding to the force and the vertical displacement for each one of the specimens. In the sequel, the diagrams corresponding to each one of the specimens from B1 to B8 in parallel with the diagram of the reference beam in Figures 6 and 7 are depicted. Figure 8 shows the diagrams for all the 9 specimens including the reference one in order to give a general comparison of the splices test results with those of the intact beam. Connections in Steel Structures V - Amsterdam - June 3-4, 4 291

6 B1 1 B B3 1 B Figure 6. Figures of the specimens and the diagrams for B1, B2, B3, B4 and. 292 Connections in Steel Structures V - Amsterdam - June 3-4, 4

7 3 2 1 B B B7 1 B Figure 7. Figures of the specimens and the diagrams for B5, B6, B7, B8 and. Connections in Steel Structures V - Amsterdam - June 3-4, 4 293

8 B1 B2 B3 B4 B5 B6 B7 B8 (REF.) Figure 8. Force-deflection diagrams for the connected beams from B1 to B8 and the reference beam. COMMENTS AND CONCLUSIONS The diagrams of the test results (Figures 6, 7, 8) for the connected beams from B1 to B8 gave a significant deflection that corresponds to a much lower force than this that corresponds to the reference curve of beam. In particular, only the 1/1 of the load used for reference beam was used to give the same deflection to the connected beams. After the end of the testing program, it was observed that all the vertical additional pieces of the web remained undeformed (intact) due to the fact that they didn t carry any loads. The latter certifies the initial assumption taken into account in the calculation of the connection. Having in mind that it is always critical to check the serviceability limit state of such beams, the failure of the specimens due to excessive deflection around the area of the splice connection is obvious. The maximum acceptable percentage according to EC is equal to 1/=.5% for total loading (4). The experimental results gave a deflection of approximately 15/=1.5% below the 1/1 of the total load. Two were the reasons for the observed significant deflections around the area of the splice connections: The first is the difference of 1 between the diameters of the holes and those of the bolts. The existence of the clearance gives a kind of freedom of sliding as soon as a small (1/1) load is applied on the beam. At this first step, the force loaded only the two additional horizontal plates on the flanges which reacted as autonomous simply supported beams instead of the full cross-section of the beam. This is the reason for the existence of linear part at the beginning of the diagrams for the connected beams from to near 15. The second reason of the observed significant deflection is due to the insertion of the thread of the bolts into the mass of the steel in the vicinity of the contact area of the holes, as shown in Figure Connections in Steel Structures V - Amsterdam - June 3-4, 4

9 As a conclusive remark it is noteworthy that the choice of the position of the splice connection must be very carefully chosen: It must be in a position along the length of the beam where the maximum moment is less than 1/1 of the maximum moment capacity of the profile HEB. Figure 9. The holes (with the traces of the insertion of the thread into the steel mass) after the experiment in an additional horizontal splice plate and in the beam flange. ACKNOWLEDGEMENTS The work reported here has been partially supported by the European Union Research and Training Network (RTN) Smart Systems. New Materials, Adaptive Systems and their Nonlinearities. Modeling, Control and Numerical Simulation, with contract number HPRN- CT NOTATION d f u f y t α diameter ultimate stress yield stress thickness distance REFERENCES (1) Ivanyi, M. & Baniotopoulos, C.C. () (eds), Semi-rigid Joints in Structural Steelwork, Springer Wien, New York, p. 3. (2) Baniotopoulos, C. C. & Wald, F. () (eds), The Paramount Role of Joints into the Reliable Response of Structures. From the Classic Pinned and Rigid Joints to the Notion of Semi-rigidity, Kluwer, Dordrecht, p. 48. (3) Kontoleon, M. J., Kaziolas, D. N., Zygomalas M.D. & Baniotopoulos, C. C. (3), Analysis of Steel Bolted Connections by Means of a Nonsmooth Optimization Procedure, COMPUTERS & STRUCTURES 81, (4) ENV (1993). Eurocode 3, Design of Steel Structures. CEN, Brussels. Connections in Steel Structures V - Amsterdam - June 3-4, 4 295

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