Quasi-static Cyclic Lateral Loading Research Articles

Cyclic Response of Nonductile Reinforced Concrete Frames with Unreinforced Masonry Infills Retrofitted with Engineered Cementitious Composites

AbstractA new seismic retrofit technique for unreinforced masonry infills in nonductile reinforced concrete frames is presented. The objective was to develop a light and easy to apply retrofit technique for the infills that both delays shear failure at the columns of the nonductile bounding frame when subjected to an earthquake by preventing severe deterioration of the infill wall, and enhances the ductility of the system. The retrofit technique uses sprayable engineered cementitious composites (ECCs), a micromechanically designed cement-based material reinforced with short, randomly distributed polymeric fibers. Four small-scale unreinforced masonry infilled nonductile reinforced concrete frames were tested under in-plane quasi-static cyclic lateral loading. One unretrofitted wall and three different retrofit schemes were evaluated. Continuous steel reinforcement was embedded in the ECC layer and a bonding agent was applied between the masonry wall and the ECC layer. In two retrofits the impact of two di...

Experimental study of retrofitted reinforced concrete shear wall and concrete-encased steel girders using a new CarbonFlex composite for damage stabilization

A bi-axially loaded shear wall and two fatigue-damaged concrete-encased steel girders are experimentally tested using a retrofit technique that utilizes a newly developed composite wrap. The composite, which is being termed “CarbonFlex,” helps to stabilize the propagation of damage, specifically fracture, in retrofitted beams and a shear wall via an energy dissipation mechanism, resulting in significant ductility and confinement, and high-strength sustainability. The CarbonFlex-retrofitted shear wall had been initially damaged to a level corresponding to 40% of its peak strength under bi-axial loading (constant vertical load and quasi-static cyclic lateral load). Following the CarbonFlex-retrofit, the capacity doubled to 80% of its original strength while exhibiting significant ductility and having tremendously improved confinement. The fatigue-damaged beams are retrofitted using conventional carbon–fiber reinforced polymers (CFRPs), and then, separately, using the new prototype CarbonFlex composite. The latter beam sustained over 68% of its peak strength following dissipation of the initial shock energy of the fractured welds of the encased steel girder; the beam also exhibited significant displacement ductility, having an ultimate displacement three times that of its CFRP counterpart.

On the quasi-static granular convective flow and sand densification around pile foundations under cyclic lateral loading

The saturated sand surrounding an offshore pile foundation under quasi-static cyclic lateral load can show the physical phenomena of macromechanical densification and convective granular flow. Based on the results from physical model tests at different geometrical scales, this paper provides a certain quantification of such phenomena and discusses their causes and consequences. The progressive sand densification leads to subsidence of the soil surface and a significant stiffening of the pile behaviour. Conversely, the ratcheting convective motion of two closed cells of soil beneath the pile-head is responsible for an endless grain migration at the soil surface, the inverse grading of the convected material and a direct shear of the sand at the distinct boundary of the revolving soil domain. In this respect, and from a macromechanical perspective considering the soil as a continuum, it appears that the convecting material tends to follow gradient lines of shear stress during its ratcheting motion. Concluding the paper, the practical relevance of these phenomena and their extrapolation to other conditions are briefly discussed.

Textile-Reinforced Mortar versus FRP as Strengthening Material for Seismically Deficient RC Beam-Column Joints

In this paper, efficiency and effectiveness of textile-reinforced mortars (TRM) on upgrading the shear strength and ductility of a seismically deficient exterior beam-column joint has been studied. The results are then compared with that of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP)-strengthened joint specimens. Five as-built joint specimens were constructed with nonoptimal design parameters (inadequate joint shear strength with no transverse reinforcement) representing an extreme case of preseismic code design construction practice of joints and encompassing the vast majority of existing beam-column connections. Out of these five as-built specimens, two specimens were used as baseline specimens (control specimens) and the other three were strengthened with TRM, CFRP, and GFRP sheets, respectively. All five subassemblages were subjected to quasi-static cyclic lateral load histories to provide the equivalent of severe earthquake damage. The response histories of control and strengthened specimens were then compared. The test results demonstrated that TRM can effectively improve both the shear strength and deformation capacity of seismically deficient beam-column joints to an extent that is comparable to the strength and ductility achieved by well-established CFRP, and GFRP-strengthening of joints.

Joint shear behaviour of reinforced concrete beam–column connections

An extensive experimental database (341 cases in total) has been constructed for reinforced concrete (RC) beam–column connections subjected to quasi-static cyclic lateral loading. All cases within the database experienced joint shear failure, either in conjunction with or without yielding of beam reinforcement. RC joint shear strength models, which are applicable to both modern and older types of beam–column connections, have been developed using the constructed database in conjunction with a Bayesian parameter estimation method. Following this same procedure established to develop the strength models, joint shear deformation models (at maximum joint shear stress) have also been developed. The proposed quantitative RC joint shear strength and deformation models indicate that the following parameters are most important towards determining joint shear strength and deformation capacity–concrete compressive strength, beam reinforcement, joint transverse reinforcement, in-plane geometry, out-of-plane geometry and joint eccentricity. Finally, the influence of these six key parameters on the RC joint shear stress against joint shear strain behaviour at peak response has been assessed.

A new statistical approach for joint shear strength determination of RC beam-column connections subjected to lateral earthquake loading

Reinforced concrete (RC) joint shear strength models are constructed using an experimental database in conjunction with a Bayesian parameter estimation method. The experimental database consists of RC beam-column connection test subassemblies that maintained proper confinement within the joint panel. All included test subassemblies were subjected to quasi-static cyclic lateral loading and eventually experienced joint shear failure (either in conjunction with or without yielding of beam reinforcement); subassemblies with out-of-plane members and/or eccentricity between the beam(s) and the column are not included in this study. Three types of joint shear strength models are developed. The first model considers all possible influence parameters on joint shear strength. The second model contains those parameters left after a step-wise process that systematically identifies and removes the least important parameters affecting RC joint shear strength. The third model simplifies the second model for convenient application in practical design. All three models are unbiased and show similar levels of scatter. Finally, the improved performance of the simplified model for design is identified by comparison with the current ACI 352R-02 RC joint shear strength model.

Behavior of tunnel form buildings under quasi-static cyclic lateral loading

In this paper, experimental investigations on the inelastic seismic behavior of tunnel form buildings (i.e., box-type or panel systems) are presented. Two four-story scaled building specimens were tested under quasi-static cyclic lateral loading in longitudinal and transverse directions. The experimental results and supplemental finite element simulations collectively indicate that lightly reinforced structural walls of tunnel form buildings may exhibit brittle flexural failure under seismic action. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in outermost shear-walls. This type of failure takes place due to rupturing of longitudinal reinforcement without crushing of concrete, therefore is of particular interest in emphasizing the mode of failure that is not routinely considered during seismic design of shear-wall dominant structural systems.

Reinforced concrete edge beam—column—slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

Reinforced concrete edge beam?column?slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

수평 반복하중을 받는 비내진상세 RC 중공구형교각의 거동특성

Scaled model tests were carried out to investigate a seismic behavior of reinforced concrete piers with hollow-rectangular section that were not detailed for seismic load. Additional lateral reinforcing bars were not provided that might be required for confinement against earthquake load. Two kinds of reinforcement details were considered for the longitudinal reinforcing bars: lap-spliced and continuous. In the lap-spliced model all longitudinal bars were lapped at the same height in a bottom plastic hinge zone. In the other model all longitudinal bars extended continuously throughout the height. The constructed models were subjected to quasi-static cyclic lateral loading in the presence of the constant vertical load. Limited ductile behavior was observed in the test of lap-spliced model and more ductile behavior was observed in the test of a continuous longitudinal reinforcement model.

콘크리트 충전 강교각의 내진 성능 평가

최근, 콘크리트 충전 강교각은 신속한 시공과 뛰어난 연성능력으로 인해 도심지에서 철근 콘크리트 교각의 대안이 되고 있다. 이러한 콘크리트 충전 강교각은 내진 설계에서도 훌륭한 성능을 발휘할 수 있으나 내진 설계의 가이드가 없어 내진 설계시 그 성능을 모두 반영하지 못하고 있는 상황이다. 이에 실제 적용을 위해 콘크리트 충전 강교각 실험으로부터 얻어진 실험치로부터 내진 설계에 지침이 될 수 있는 가이드를 제시하고자 한다. 콘크리트 충전 강교각과 일반 강교각의 연성 능력을 평가하기 위해 준 정적 반복 재하 실험을 수행하고, 지진 거동을 검증하기 위해 고베 지진을 입력 데이타로 한 유사 동적 실험을 수행한다. 콘크리트 충전 강교각은 일반 강교각에 비해 만족할 만한 연성도와 강도를 보이고, 동적 거동은 상대적으로 큰 이력감쇠를 증명한다. 실험으로 얻어진 데이터를 근거로 하여 콘크리트 충전 강교각의 내진 성능을 정량화 하고, 탄성응답 스펙트럼에 의한 지진응답 수정계수법과 유효 점성 감쇠를 이용한 성능 곡선 및 요구 스펙트럼에 의한 성능기초 설계법의 비교를 통하여, 콘크리트 충전 강교각과 일반 강교각의 내진 성능을 평가한다. 이러한 내진 성능 평가를 기초로 하여, 일반 강교각과 더불어 내진 설계에 적용할 수 있는 콘크리트 충전 강교각의 지진응답 수정계수를 제시한다. A recent development, a concrete-filled steel(CFS) pier is an alternative to a reinforced concrete bridge pier in an urban area, because of its fast construction and excellent ductility against earthquakes. The capacity of CFS piers has not been used to a practical design, because there is no guide of a seismic design for CFS piers. Therefore, the guide of a seismic design value is derived from tests of CFS piers in order to apply it to a practical seismic design. Steel piers and concrete-filled steel piers are tested with constant axial load using quasi-static cyclic lateral load to check ductile capacity and using the real Kobe ground motion of pseudo-dynamic test to verify seismic performance. The results prove that CFS piers have more satisfactory ductility and strength than steel piers and relatively large hysteretic damping in dynamic behaviors. The seismic performance of steel and CFS piers is quantified on the basis of the test results. These results are evaluated through comparison of both the response modification factor method by elastic response spectrum and the performance-based design method by capacity spectrum and demand spectrum using effective viscous damping. The response modification factor of CFS piers is presented to apply in seismic design on a basis of this evaluation for a seismic performance.

Seismic Performance of Rectangular Bridge Columns with Moderate Confinement

This study is part of a project to develop detailing guidelines for reinforced concrete bridge columns and walls in areas of low to moderate seismicity. The work presented examines the ductility and behavior of rectangular reinforced concrete columns with moderate confinement. Four half-scaled rectangular bridge columns were built and tested. The transverse reinforcement ratios provided in the strong direction of the column specimens corresponded to 46% and 60% of the minimum lateral reinforcement required by the American Association of State Highway and Transportation Officials for seismic detailing. Each specimen was tested under constant axial load while subjected to quasistatic cyclic lateral loading in the column strong direction. The axial load indexes were 10% and 25%. The specimens exhibited displacement ductilities ranging between 5 and 7. Based on analytical and experimental results, an equation for designing the confinement steel for target ductility is presented.

EERI Annual Student Paper Award Confinement of Rectangular Bridge Columns in Moderate Seismic Areas

The work presented in this paper examines the ductility and behavior of rectangular reinforced concrete bridge columns with moderate confinement. Four half-scaled rectangular columns were built and tested. The transverse reinforcement ratios provided in the strong direction of the column specimens corresponded to 46 percent and 60 percent of the minimum lateral reinforcement required by AASHTO for seismic detailing. Each specimen was tested under constant axial load while subjected to quasi-static cyclic lateral loading in the column strong direction. The axial load indexes were 10 percent and 25 percent. The specimens exhibited displacement ductilities ranging between 5 and 7. Based on analytical and experimental results, a simple design equation relating the amount of confinement steel to attainable displacement ductility was developed.

Assessment and Retrofit of a Reinforced Concrete Bridge Pier for Seismic Resistance

Typical structural deficiencies in some reinforced concrete bridges designed for seismic resistance before current seismic codes were introduced are briefly outlined. Results of simulated seismic load tests conducted on the critical region of a reinforced concrete bridge pier designed in New Zealand in 1936 are presented. The tests involved the application of compressive axial loading and quasi-static cyclic lateral loading to a full-scale subassemblage representing the column-cap beam region of the as-built pier. Subsequent loading tests were conducted on the pier retrofitted mainly by the addition of steel plates welded to the ends of the plain round longitudinal bars to improve anchorage. The improved bar anchorage enabled the pier to develop its full theoretical flexural strength, but the considerable loss of stiffness due to bond degradation which occurred in the initial test on the as-built pier was not restored.

Single Pile Response to Cyclic Lateral Load

An analysis is presented for the deflection of a pile in clay subjected to quasi-static cyclic lateral loading. This analysis is an extension of the elastic continuum analysis for static pile response, and allows for the reduction of soil modulus and yield pressure with increasing cyclic strain or deflection. A number of theoretical solutions are presented to illustrate the factors influencing the increase in deflection and bending moment in the pile with increasing cycles and cyclic load level. Some of these solutions are presented in dimensionless form as correction factors which may be applied to the computed static response of a pile. Some comparisons are made between the theoretical behaviour and that measured in field tests, and these demonstrate that the theory reproduces the observed characteristics of behaviour of the pile. They also give an indication of the order of magnitude of some of the key variables in the cyclic response analysis.