Sustainable and deconstructable flush end plate semi-rigid beam to column composite joints

Transcription

1 Southern Cross University 23rd ustralasian Conference on the Mechanics of Structures and Materials 214 Sustainable and deconstructable flush end plate semi-rigid beam to column composite joints taei University of New South Wales M. Bradford University of New South Wales X Liu University of New South Wales Publication details taei,, Bradford, M & Liu, X 214, 'Sustainable and deconstructable flush end plate semi-rigid beam to column composite joints', in ST Smith (ed.), 23rd ustralasian Conference on the Mechanics of Structures and Materials (CMSM23), vol. II, Byron Bay, NSW, 9-12 December, Southern Cross University, Lismore, NSW, pp ISBN: epublications@scu is an electronic repository administered by Southern Cross University Library. Its goal is to capture and preserve the intellectual output of Southern Cross University authors and researchers, and to increase visibility and impact through open access to researchers around the world. For further information please contact epubs@scu.edu.au.

2 23rd ustralasian Conference on the Mechanics of Structures and Materials (CMSM23) Byron Bay, ustralia, 9-12 December 214, S.T. Smith (Ed.) SUSTINBLE ND DECONSTRUCTBLE FLUSH END PLTE SEMI- RIGID BEM TO COLUMN COMPOSITE JOINTS. taei* Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, UNSW ustralia, Sydney, NSW, 252, ustralia. (Corresponding uthor) M.. Bradford Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, UNSW ustralia, Sydney, NSW, 252, ustralia. X. Liu Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, UNSW ustralia, Sydney, NSW, 252, ustralia. BSTRCT Composite steel-concrete floor systems are a ubiquitous structural steel framing configuration for commercial and institutional buildings, exploiting the strengths of both reinforced concrete and structural steel symbiotically in a complementary fashion. However, within paradigms related to minimisation of carbon emissions and maximisation of product recycling, these composite systems are problematic on a number of fronts. This paper describes the results of three full-scale sustainable flush end plate semi-rigid beam-to-column joints with deconstructable pre-tensioned bolted shear connectors. In this system, precast green concrete (GC) slabs associated with reduced CO 2 emissions during their manufacture are attached compositely to the steel beam via pre-tensioned bolted shear connectors that are readily deconstructed at the life-end of the building. The test results show that these composite joints have credible rotation and moment capacities according to EC3 and EC4, and that fracture of the joint occurs when substantial rotational deformation has developed. KEYWORDS Composite joints, bolted shear connectors, deconstructability, sustainability. INTRODUCTION The traditional flush end plate semi-rigid composite connection is a popular and widely-adopted choice for connecting a composite beam to a column. This particular connection has several advantages, such as its ease of construction as well as being economical compared to a rigid connection. dditional to these benefits, the rigidity of this connection allows for adequate moment distribution in the frame. These composite connections have higher initial stiffness and moment capacity as well as rotational capacity compared with bare steel connections, owing to the contribution of the reinforcing bars located in the slab. The tensile forces induced are resisted by the upper bolts and the reinforcing bars and the compressive forces are resisted by the steel beam. The reinforcing bars contribute significantly to the strength and stiffness of the connection. Within current paradigms related to minimising carbon emissions and maximising product recycling, traditional composite systems are problematic on a number of fronts. Firstly, composite action between the concrete slab and steel beam in a building frame is typically achieved by headed stud This work is licensed under the Creative Commons ttribution 4. International License. To view a copy of this license, visit 1

3 shear connectors that are welded to the top flange of the steel beam to produce robust shear connection, but their demolition necessarily is associated with much waste and uses considerable energy. Secondly, the slab is usually cast in situ onto profiled steel decking with conventional reinforcement placed on site, which is time consuming and labour intensive and which can increase the construction costs considerably. Thirdly, these systems mostly utilise concrete derived from ordinary Portland cement, whose manufacture is one of the largest global sources of CO 2 emissions. The deconstructable and sustainable composite beam-to-column joints proposed in this research represent a novel structural system. Combining precast GC slabs with steel elements by using a deconstructable or demountable technique may minimise these problems and concerns associated with traditional composite structures. The main advantages of this more environmentally-friendly construction are that the precast GC concrete units, steel frames and the high tensile bolts are manufactured off site and share the quality control, accuracy and reliability of factory production and which may lead to savings associated with reduced construction times. Furthermore, this building system can be deconstructed at the end of its service life with the minimisation of waste and the maximisation of component recycling. Pre-tensioned high-strength bolts installed through holes in the precast slabs into pre-drilled holes in the steel beam produce a composite flooring system that can be deconstructed at the end of life of the structure (Bradford and Pi 212a,b, 213; Rowe and Bradford 213; taei and Bradford 213). Marshall et al. (1971) appear to be the first researchers to have reported the use of bolted shear connection, but the context of the usage is not clear. Dallam (1968) and Kwon et al. (21) conducted some experimental research on using post-installed bolted shear connectors. However, no research appears to have been reported on semi-rigid flush end plate composite joints with deconstructable bolted shear connectors. This paper describes the results of two full-scale sustainable and deconstructable flush end plate semi-rigid beam-to-column composite joints. In this system, precast GC slabs having reduced CO 2 emissions during their manufacture are attached compositely to the steel beam via pre-tensioned bolted shear connectors and the composite beam is connected to I-section columns. Based on the experimental results, the structural behaviour of these new systems is assessed and investigated. In addition to these two composite joint tests and as a control, a beam-to-column joint without a precast composite slab was also tested and the results are reported. The test results show that these composite joint configurations have reasonable rotation and moment capacities according to EC3 and EC4, and that fracture of the joint occurs when substantial rotational deformation has developed. EXPERIMENTL PROGRM Three full-scale beam-to-column joints were designed and constructed in a cruciform arrangement to simulate the internal joint in a semi rigid frame and to evaluate the stiffness, moment capacity and rotation capacity of these prototype joints. The geometric and design details are illustrated in Figure 1. novel methodology of shear connection was adopted by using pre-tensioned bolted shear connectors to attach precast concrete slabs to the top flange of the steel beams. Specimens 1 and 2 were designed as composite joints (CJ) and Specimen 3, which was a non-composite joint, was designed as a control test specimen for comparison of the composite joint tests. ll specimens consisted of a 46UB82.1 steel beam and a 25UC89.5 steel column. 12 mm flush end plate welded at the end of steel beam was connected to the flange of the column using 4 M24 grade 8.8 bolts. plates were welded to the column web at the level of the bottom and top flanges of the beam to prevent bending of the column flanges in tension and failure of the column web in compression, and M24 grade 8.8 bolts were used as shear connectors at a spacing of 12 mm. Six N16 bars provided reinforcement to the slab. Figure 2(a) shows CJ1, which comprised of one precast GC concrete slab attached to the top flange of the steel beam with pre-tensioned bolted connectors. The longitudinal reinforcement ratio for this slab was.9%. Six effective longitudinal N16 reinforcing bars were placed in the top layer of the precast slab. In the bottom layer, N1 bars were distributed similarly to the top layer, but they were terminated CMSM

4 near the column face to prevent them from contributing to the moment resistance. Two layers of N1 bars were also used transversely to prevent longitudinal splitting of the slab. 331 M2 Bolts Washer 6x6x6 mm GC Precast Slab Reaction Reaction Steel beam (46 UB 82.1) 6N16 effective or M2 Flush End plate 51x22x12 4 M24 Bolts 6 N16 effective or 2X(22x12x16 mm) End plate 4 M24 bolts 51X22X12 mm Load Steel column 4X(22x12x16 mm) Elevation View H-section Column (a) Plate 1X8x8mm Pre-tensioned bar M2 Bolts Washer 6x6x6 mm 331 GC Precast Slab Reaction Reaction Plastic pipe 6N16 effective M N16 effective Plastic pipe nchor Head and Wedges Steel beam (46 UB 82.1) or Flush End plate 51x22x12 4 M24 Bolts 2X(22x12x16 mm) End plate 4 M24 bolts 51X22X12 mm Load Steel column 4X(22x12x16 mm) Elevation View Section - H-section Column nchor Head and Wedges 6N16 effective Plate 1X8x8mm Duct x276 H-section Column Plane View(Reinforcing Bars) (b) Figure 1. Details of joints: (a) CJ1; (b) CJ2 CJ2 represents an alternative deconstructable option, as illustrated in Figure 2(b), comprising of two precast GC slabs juxtaposed on the top flange of the steel beam and attached to it by means of bolted shear connectors. For these opposing precast slabs, the top layer of N16 reinforcing bars was not embedded at casting. Rather, pre-formed ducts (formed using plastic tubes) were provided at the location of top reinforcement, and N16 reinforcing bars were installed into these after assembly of the CMSM

5 panels. The reinforcing bars, as shown in Figure 2(c), were post-tensioned to approximately 1% of their axial load capacity before testing. Steel Joint 3 (SJ3) was designed as the reference and control test specimen, being similar to the two composite joints but without a precast concrete slab. LODING PROCEDURE ll specimens were loaded vertically under displacement control by using a hydraulic jack. In order to check the test set-up, a small load of about 1% of the predicted ultimate capacity of the specimens was applied before the main testing. During this loading, the performance of the components of the specimens and the instrumentation was monitored. The specimens were then reloaded, and the load was increased monotonically until failure of the specimen and no further loading could be sustained. Three loading rates were used sequentially during the loading, viz..3 mm/min,.6 mm/min and 1.2 mm/min. The rest was then terminated when the load started to fall significantly. (a) (b) (c) Figure 2. (a) CJ1 ready to be tested; (b) ssemblage of the steel beam and precast slab (CJ2), (c) CJ2 ready to be tested. TEST RESULTS Pre-formed ducts Post-tensioned bars Moment-rotation and load-deflection curves for the three joints are shown in Figure 3, and the results of these tests are summarised in Table 2. s can be seen, maximum loads of about 55, 498 and 25 kn with corresponding deflections of about 56, 55 and 5 mm were recorded for CJ1, CJ2 and SJ3 respectively, and all specimens behaved non-linearly before failure. Moment capacities of about 63, 622 and 256 knm with rotation capacities of about 44, 42 and 38 mrad were recorded for CJ1, CJ2 and SJ3 respectively. It also can be seen that composite action has a significant effect on the behaviour of the joints, with the ultimate moment capacities of CJ1 and CJ2 being 2.46 and 2.43 times that of SJ3 respectively, which means that the precast concrete slabs improve significantly the moment capacities of the joints. The rotation capacities of both composite joints are also slightly higher than the noncomposite joint. Importantly, although the moment and rotation capacity of CJ1 and CJ2 are almost the same, the behaviour of these two composite joints is different. Similar initial stiffnesses in both composite joints were observed, but the secant stiffness of CJ2 is smaller than that of CJ1. The initial stiffness of SJ3 is much smaller than those of CJ1 and CJ2. The mode of failure for all three specimens was bolt fracture in the tension zone of the connections. The evolution of the end slip for CJ1 and CJ2 is shown in Figure 4(a). It can be seen that the final slips between the precast concrete slab for CJ1 and CJ2 are 4. and.2 mm respectively, and so it can be concluded that the slip is almost zero when two precast concrete slab units were used in composite joints. In contrast, when one unit is used, the magnitude of slip at the end of composite beam is almost same as clearance between the holes in steel beam and precast concrete slab and bolted shear connectors. Figure 4(b) shows the strain in the longitudinal reinforcing bars measured during the tests for CJ1 and CJ2. The behaviour of the bars in these two composite joint is completely different as shown in Figure CMSM

6 Load (KN) Load (KN) Yield Strain Load (KN) Moment (KN.m) 4(b). It also can be seen that the average strain for the reinforcing bars in CJ1 exceed the yield strain of 275 microstrain slightly. In contrast, the average strain for the reinforcing bars in CJ2 exceeds the yield strain before the ultimate load is reached significantly, because these bars have an initial pretension. (a) (b) Figure 3. (a) Load-deflection relationship for CJ1, CJ2 and SJ3, (b) Moment-rotation relationship for CJ1, CJ2 and SJ3. (a) (b) Figure 4. (a) Load-slip response of bolted shear connectors for CJ1 and CJ2, (b) verage reinforcing bar strain at the mid-span for CJ1 and CJ2. Specimen Table 1. Test result of composite joints and non-composite joint. Maximum Maximum Moment Rotation Maximum load deflection capacity capacity slip (kn) (mm) (knm) (mrad) (mm) Mode of failure CJ Bolt fracture CJ Bolt fracture SJ N.. Bolt fracture CONCLUSIONS CJ 1 CJ 2 SJ Deflection (mm) CJ 1 CJ Slip (mm) In this paper, the results of two full-scale sustainable and deconstructable flush end plate semi-rigid beam-to-column composite joints were reported. Based on the experimental results, the structural behaviour of these novel systems that used precast slabs and bolted shear connection were assessed and investigated. The pertinent variable was the shape of the precast concrete slab, viz. a monolithic slab and two joined slabs. In addition, a beam-to-column joint without a slab was also conducted and the results were reported. The significant findings from these full-scale tests underpinned the following conclusions: In order to allow for plastic analysis and design, the rotation capacity of the joint must be higher than 3 mrad according to EC4. The semi-rigid beam-to-column composite joint with 7 CJ 1 CJ 2 SJ Rotation (mrad) CJ1 CJ2 1 2 Strain (µe) CMSM

7 deconstructable bolted shear connectors can provide a higher rotation (about 1.5 times) of that specified by the design code. The ultimate moment capacities of the composite joints were about 2.5 times the ultimate moment capacity of the non-composite joint, indicating that the precast concrete slabs attached by bolted shear connectors improved the moment capacities of the joints significantly. The rotation capacities of the composite joints were slightly higher than that of the non-composite joint. The ultimate slip was found to be almost zero when two precast concrete slab units were used in the composite joints. In contrast, when one precast concrete slab unit was used, the magnitude of slip at the end of composite beam was almost same as the clearance between the holes in the steel beam and the precast concrete slab and the diameter of the bolted shear connectors. The slip between the slab and the steel beam causes decreasing strains in the reinforcing bars which leads to decreasing of the load in the bars and increasing the load in the bolts located in the tension part of the connection. CKNOWLEDGMENTS The work in this paper was supported by the ustralian Research Council through an ustralian Laureate Fellowship (FL63) awarded to the second author. REFERENCES taei. and Bradford M.. (213) FE Modelling of sustainable semi-rigid flush end plate composite joints with deconstructable bolted shear connectors, Composite Construction CCVII, Palm Cove, Queensland, July. Bonilla Rocha J.D., rrizabalaga E.M., Larrua Quevedo R. and Recarey Morfa C.. (212) Behavior and strength of welded stud shear connectors in composite beam, Revista Facultad de Ingeniería Universidad de ntioquia, Vol. 63, pp (in English). Bornstein R., Song T. and Mukhin V. (213) Laboratory assessment of drying shrinkage of concretes containing shrinkage reducing agents compared with a new low shrinkage concrete, Concrete 213, Gold Coast, Queensland, Paper 188. Bradford M.. and Pi Y.-L. (212a) Numerical modelling of deconstructable composite beams with bolted shear connectors, Conference on Numerical Modeling Strategies for Sustainable Concrete Structures, ix-en-provence, France, II-2, pp Bradford M.. and Pi Y.-L. (212b) Numerical modelling of composite steel-concrete beams for lifecycle deconstructability, 1st International Conference on Performance-Based and Life-Cycle Structural Engineering, Hong Kong, pp Bradford M.. and Pi Y.-L. (213) Nonlinear elastic-plastic analysis of composite members of highstrength steel and geopolymer concrete, Computer Modeling in Engineering and Sciences 232, pp Dallam L.N. (1968) Pushout Tests with High Strength Bolt Shear Connectors. Report for Missouri State Highway Department, Department of Civil Engineering, University of Missouri-Columbia, Missouri, US. Dallam L.N. and Harpster J.L. (1968) Composite Beam Tests with High-Strength Bolt Shear Connectors. Report for Missouri State Highway Department, Department of Civil Engineering, University of Missouri-Columbia, Missouri, US. Kwon G., Engelhardt, M.D. and Klinger, R.E. (21) Behavior of post-installed shear connectors under static and fatigue loading, Journal of Constructional Steel Research, Vol. 66, pp Marshall W.T., Nelson H.M. and Banerjee, H.K. (1971) n experimental study of the use of highstrength friction-grip bolts as shear connectors in composite beams, The Structural Engineer, Vol. 49, pp Rowe M. and Bradford M.. (213) Partial shear interaction in deconstructable composite steelconcrete composite beams with bolted shear connectors, International Conference on Design, Fabrication and Economy of Welded Structures, Miskolc, Hungary, pp CMSM