Experımental and fınıte element analyses punchıng shear Behavıor of two way reınforced concrete slabs havıng Openıngs and retrofıtted wıth cfrp sheets

Bu tez çalışmasında kare geometriye sahip olan boşluklar içeren 8 adet betonarme döşeme dıştan yapıştırılan CFRP şeritler kullanılarak güçlendirilmiştir. Döşemelerin alt ve üst yüzlerinde ızgara şeklinde donatılar kullanılmıştır. Döşemelerin güçlendirilmesi için döşeme alt yüzünde ve boşluk köşelerinde dıştan yapıştırılan CFRP şeritler kullanılmıştır. Pratik şekilde uygulanan güçlendirme işleminin yapıları kullanan insanlara rahatsızlık vermeden, yapının görünüşünü bozmadan ve çok zaman almadan uygulanabilir olması bu sistemin CFRP kullanılarak uygulanan diğer güçlendirme yöntemlere göre avantajlarıdır. Yapılan deneyler sonrasında, uygulanan güçlendirme sisteminin başarılı sonuçlar verdiği, boşluksuz deney elemanının zımbalama dayanımının pratik güçlendirme işlemi sayesinde ortalama olarak yakalandığı görülmüştür. Deney çalışmasından elde edilen sonuçlar şartnameler tarafından önerilen denklemler ile karşılaştırılmıştır. Denklemlerin genelde zımbalama kapasitelerini deneysel sonuçlardan daha büyük verdikleri görülmüştür. Deney elemanlarının üç boyutlu sonlu eleman analizleri de bu çalışma kapsamında gerçekleştirilmiştir. Kurulan detaylı sonlu eleman modellerinde, deneylerde gözlenen köşe kalkması davranışı ve dıştan yapıştırılan CFRP şeritlerin beton yüzeyinden sıyrılması dikkate alınmıştır. Sonlu eleman analizlerinden elde edilen sonuçlar deneysel çalışmanın sonuçları ile karşılaştırılarak sunulmuştur. Karşılaştırmalardan ise sonlu eleman modellerinin CFRP şeritlerle güçlendirilmiş kirişsiz döşemelerin zımbalama dayanımlarını tahmin etmede genel olarak başarılı olduğu görülmüştür. Buna dayanarak, detaylı şekilde oluşturulmuş sonlu eleman modellerinin, CFRP şeritlerle güçlendirilmiş boşluklu döşemelerin zımbalama dayanımlarını tahmin etmede kullanılabileceği düşünülmektedir.In this thesis 8 reinforced concrete slabs with square shaped openings are retrofitted with externally bonded CFRP sheets. The slabs are constructed with two layers of mesh reinforcement located in the top and bottom surfaces of the slabs. The test specimens are retrofitted with CFRP strips located under the slab and U shaped CFRP strips located at the corners of the openings. Main advantages of the proposed retrofitting system with respect to the other retrofitting procedures employed using CFRP materials are the short application time, ease of application due to the absence of anchorage mechanisms and limited or no aesthetic impact on the retrofitted structure. From the experimental results, it is observed that the proposed retrofitting system increased the average punching shear capacity of the test specimens to the punching shear capacity of the reference specimen without any openings. The experimental results are also compared with the available code equations. From the comparisons it is clear that the equations proposed by the codes generally overestimated the experimental punching shear capacities of the test specimens. 3 dimensional finite element analyses of the test specimens are also conducted in scope of this study. In the detailed finite element models, the lift of corners of the test specimens and bond slip behavior of CFRP strips are included. The results of the finite element analyses are comparatively presented together with the experimental results. From the comparisons, it is observed that, in general, the finite element models accurately estimated the punching shear capacities of the test specimens. In relation to this it is believed that detailed finite element models may be used to estimate the punching shear capacities of the reinforced concrete slabs having openings and retrofitted with CFRP sheets

A(p)/V-p specific inelastic displacement ratio for the seismic response estimation of SDOF structures subjected to sequential near fault pulse type ground motion records

This research study is focused on an improved statistical equation proposed to estimate the inelastic displacement ratio, C-1, of structures subjected to sequential (pre-shock, main shock, after shock) pulse type near fault (NF) ground motions. Proposed equation considers the effects of fundamental vibration period of the structure, T, lateral strength ratio, R, and frequency content of the design earthquake on the variation of the response. Frequency content of the design earthquake, represented by the A(p)/V-p ratio (i.e. ratio of peak ground acceleration (A(p)) to peak ground velocity (V-p)), is a function of the earthquake magnitude, distance to fault, faulting mechanism and site class. In scope of the study statistical analyses were conducted to develop a simple and accurate statistical equation to estimate the C-1 of structures subjected to sequential pulse type NF ground motions. From the results of the study it was observed that the C-1 values obtained from the proposed equation are, generally, in good agreement with the calculated exact results. Also, the C-1 and T relationships were plotted together with those of a former study to clearly show the detrimental effect of the sequential ground motion loading in terms of amplified displacement demands

Betonarme binaların kesme bağlantı elemanlı çelik çubuklar kullanılarak deprem güçlendirmesi.

The catastrophic damage to the infrastructure due to the most recent major earthquakes around the world demonstrated the seismic vulnerability of many existing reinforced concrete buildings. Accordingly, this thesis is focused on a proposed seismic retrofitting system (PSRS) configured to upgrade the performance of seismically vulnerable reinforced concrete buildings. The proposed system is composed of a rigid steel frame with chevron braces and a conventional energy dissipating shear link. The retrofitting system is installed within the bays of a reinforced concrete building frame. A retrofitting design procedure using the proposed seismic retrofitting system is also developed as part of this study. The developed design methodology is based on performance-based design procedure. The retrofitting design procedure is configured to provide a uniform dissipation of earthquake input energy along the height of the reinforced concrete building. The PSRS and a conventional retrofitting system using squat infill shear panels are applied to an existing school and an office building. Nonlinear time history analyses of the buildings in the original and retrofitted conditions are conducted to assess the efficiency of the PSRS. The analyses results revealed that the PSRS can efficiently alleviate the detrimental effects of earthquakes on the buildings. The building retrofitted with PSRS has a more stable lateral force-deformation behavior with enhanced energy dissipation capability than that of the one retrofitted with squat infill shear panels. For small intensity ground motions, the maximum inter-story drift of the building retrofitted with the PSRS is comparable to that of the one retrofitted with squat infill shear panels. But for moderate to high intensity ground motions, the maximum inter-story drift of the building retrofitted with the PSRS is considerably smaller than that of the one retrofitted with squat infill shear panels.M.S. - Master of Scienc

Evaluation of displacement coefficient method for seismically retrofitted buildings with various ductility capacities

This research study is aimed at evaluating the accuracy of the displacement coefficient method (DCM) of FEMA 440 and associated nonlinear static procedure (NLSP) for actual buildings with soft story mechanism and various ductility capacities. The DCM and associated NLSP are evaluated using two existing seismically vulnerable buildings with soft story mechanism. The buildings are first retrofitted using a ductile steel-brace-link system to represent those with good ductility capacity and then retrofitted with RC squat infill shear panels (SISPs) to represent those with relatively poor ductility capacity. The evaluation of the DCM of FEMA 440 and associated NLSP is then performed by comparing the roof displacements (target displacements), maximum interstory drifts, and maximum plastic hinge rotations of the original and retrofitted buildings obtained from NLSP (at the target displacement level of DCM) with those obtained from nonlinear response history (NRH) analyses for three different seismic performance levels. It is observed that the DCM, and hence, the NLSP fail to accurately predict the NRH analyses results mainly due to uncertainties in the coefficient C1 of the DCM in the short period range, the inability of the DCM to capture the failure of structural members beyond a certain lateral displacement or plastic rotation limit and associated soft story mechanism. Copyright (c) 2013 John Wiley & Sons, Ltd

A(P)/V-P specific inelastic displacement ratio for seismic response estimation of structures

In this study, two new site specific statistical equations are proposed to estimate the inelastic displacement ratio, C-1 of structures subjected to far fault (FF) and near fault (NF) ground motions. The proposed equations consider the effects of fundamental vibration period of the structure, T, lateral strength ratio, R and frequency content of the design earthquake record represented by the A(p)/V-p ratio (or T-0=2/A(p)/V-p), which is a function of the earthquake magnitude, distance to fault, faulting mechanism and site class. It was observed that the C-1 values obtained from the proposed equations are in good agreement with the calculated results. The flare of the plotted C-1 vs. T/T-0 curves enables the proposed equations to cover nearly all the calculated C-1 data range and give satisfactory results. However, the curves obtained using the C-1 equations of several codes and those available in the literature do not cover the whole calculated C-1 data range and generally give unconservative results (smaller C-1 values) especially in the shorter period range. For the longer period range, the predictions of C-1 obtained from the proposed equation and the ones available in the literature are in good agreement with the calculated C-1 data. Copyright (c) 2014 John Wiley & Sons, Ltd