Abstract
This paper presents experimental and numerical studies carried out on two-story reinforced concrete (RC) frames having weaker beam-column joints, which were retrofitted with reinforced concrete haunches to avoid joint panel damage under seismic actions. The design philosophy of the retrofit solution is to allow beam-column members to deform inelastically and dissipate seismic energy. Shake table tests were performed on three 1 : 3 reduced scale two-story RC frame models, including one model incorporating construction deficiencies common in developing countries, which was retrofitted with two retrofit schemes using RC haunches. The focus of the experimental study was to understand the seismic behaviour of both as-built and retrofitted models and obtain the seismic response properties, i.e., lateral force-displacement capacity curves and time histories of model response displacement. The derived capacity curves were used to quantify overstrength and ductility factors of both as-built and retrofitted frames. Finite element- (FE-) based software SeismoStruct was used to develop representative numerical models, which were calibrated with the experimental data in simulating the time history response of structure roof displacement and in predicting peak roof-displacement and peak base shear force. Moreover, the FE-based numerical models were subjected to a suite of spectrum natural accelerograms, linearly scaled to multiple intensity levels for performing incremental dynamic analysis. Lateral force-displacement capacity and response curves were developed, which were analyzed to calculate the structure ductility and overstrength factors. The structure R factor is the product of ductility and overstrength factors, which exhibited substantial increase due to the proposed retrofitting technique. A case study was presented for the seismic performance assessment of RC frames with/without RC haunches in various seismic zones using the static force procedure given in seismic code and using response modification factor quantified in the present research.
Highlights
Non-seismic design or poorly built RC frames have exhibited significant vulnerability in recent earthquakes, and in experimental tests, against seismic actions [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
Experimental pullout tests conducted on embedded rebars in concrete cylinders with similar epoxy suggested the minimum embedded length of 6 inches (152.40 mm) in prototype that reduced to 2 inches (50 mm) in test model. e development length requirement of rebars was based on the actual pullout tests. e rebar insertion followed pouring of concrete in a special fabricated formwork. e haunches were cured for 28 days to attain their desired strength
Conclusions and Recommendations e following conclusions were drawn on the basis of experimental shake table tests performed on as-built and retrofitted RC frames with reinforced concrete haunches: Noncompliant RC frame incorporating construction deficiencies, i.e., having concrete with low compressive strength, beam/column members having reduced longitudinal and transverse reinforcements, and joints lacking lateral ties, was observed with extensive damage in beam-column joints and columns. is reduced the lateral strength and ductility ratio of RC frames. e overstrength factor Ω0 was found equal to 2.15 and ductility factor Rμ was found equal to 1.35. is indicates a reduction of 23% and 56% in overstrength and ductility factors, respectively, in comparison to the values suggested in the Building Code of Pakistan
Summary
Non-seismic design or poorly built RC frames have exhibited significant vulnerability in recent earthquakes, and in experimental tests, against seismic actions [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. Despite the recent work on haunch retrofitting technique, there is still lack of significant amount of data to help the structural engineers design or validate haunch-retrofitted structures using static force procedure given in national seismic codes. One such piece of information required is the response modification factor R, essential for structural design and assessment in various seismic zones
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