RC Walls Research Articles

鉄骨屋根体育館におけるRC片持壁付架構の応答評価

In the 2011 Tohoku Earthquake, a large number of school gymnasia suffered damage and were unable to be used as shelters. One of the most typical damage observed in steel roof gymnasia supported by RC frame were failures at the anchored connections of steel roof bearings on RC frames. In the previous paper, we have discussed on the response of cantilevered RC walls supporting steel roofs using analytical model of a damaged gymnasium in the 2011 Tohoku earthquake, and the obtained analytical results were evaluated on the observed damage. In this paper, the action of cantilevered RC walls supporting steel roofs is investigated using parametric analysis model of various school gymnasia. Based on the analytical results, a simple response evaluation method for the cantilevered frames and reaction forces at roof bearings are proposed.

Assessment of Seismic Performance of High-Rise Thin RC Wall Buildings in Lima, Peru Using Fragility Functions

The actual behavior of thin RC wall high-rise buildings during an earthquake in Lima, Peru, and the associated seismic loss is unknown. This type of building was assessed done using analytical fragility functions. The numerical model was based on full-scale tests done in Lima, Peru. Nonlinear dynamic response analysis was performed using records simulated for Lima. The damage ratio was estimated for four damage states and fragility functions were obtained assuming that the damage ratio followed log-normal distributions. Seismic performance was evaluated by considering the probability of different damage states for three seismic hazard levels. It was found that highrise buildings present a low probability of collapse in severe earthquakes.

Damage index based on stiffness degradation of low‐rise RC walls

SummaryWidely used damage indices, such as ductility and drift ratios, do not account for the influences of the duration of strong shaking, the cumulative inelastic deformation or energy dissipation in structures. In addition, the formulation and application of most damage indices have until now been based primarily on flexural modes of failure. However, evidence from earthquakes suggests that shear failure or combined shear‐flexure behavior is responsible for a large proportion of failures. Empirical considerations have been made in this paper for evaluating structural damage of low‐rise RC walls under earthquake ground motions by means of a new energy‐based low‐cycle fatigue damage index. The proposed empirical damage index is based on the results of an experimental program that comprised six shake table tests of RC solid walls and walls with openings; results of six companion walls tested under QS‐cyclic loading were used for comparison purposes. Variables studied were the wall geometry, type of concrete, web shear steel ratio, type of web shear reinforcement, and testing method. The index correlates the stiffness degradation and the destructiveness of the earthquake in terms of the duration and intensity of the ground motions. The stiffness degradation model considers simultaneously the increment of damage associated to the low‐cycle fatigue, energy dissipation, and the cumulative cyclic parameters, such as displacement demand and hysteretic energy dissipated. Copyright © 2014 John Wiley & Sons, Ltd.

Retrofitting of a Double Unit Tunnel Form Building Using Additional RC Wall, Steel Angle and CFRP

Tunnel form construction is widely known as modern construction method that enables the construction of horizontal and vertical elements simultaneously. It is quickly construct low cost, high quality and earthquake safe to construct cellular buildings. Main objective of this study is to determine the seismic retrofitting performance of a double unit tunnel form building when retrofitted using additional RC wall, steel angle and Carbon Fiber Reinforced Polymer (CFRP) when tested under in-plane lateral cyclic loading. A comparison of tunnel form building was made before and after retrofitting in terms of lateral strength, stiffness, ductility and equivalent viscous damping. Result indicates that retrofitting method using additional RC wall, steel angle and CFRP was able to increase the lateral strength, ductility and equivalent viscous damping under in-plane lateral cyclic loading. The result also shows the effectiveness of additional RC wall, steel angle and CFRP in improving the shear resistances and deformation capacities of concrete structures and delaying their stiffness degradation under earthquake loading.

Inelastic Dynamic and Non-Linear Static Seismic Performance of a Building with RC Walls that Collapsed in the Chile’s Earthquake of February 2010 and a Building with RC Concrete Frame Designed in the Mexico City

The objectives in this paper are the followings: evaluate the seismic performance of the three buildings and compare the elastic and inelastic seismic responses of the buildings, calculated with the records CCH-NS (Chilean earthquake 2010) and SCT-EW (Mexican earthquake 1985) of the cases of strengths elastic and inelastic with nominal strength and over-strength of each model. The building 1 is a real case of a concrete wall building that collapsed during the Chilean earthquake of February 27, 2010. The building 2 was analyzed and designed with the Chilean Norm “Seismic Design of Buildings” (NCH-433) and “Reinforced Concrete–Design and Calculus Requirements” (NCH-430). The analyses and design of the building 3 was realized with the Mexican Norms “Complementary Technical Norms for seismic design” (NTC-Seismic), “Complementary Technical Norms for Design and Construction of Concrete Structures” (NTC-Concrete) of the “Code of Constructions for the Federal District” (RCDF-04). The elastic and inelastic seismic responses of each building were calculated with the step by step dynamic method. Should be avoided that the fundamental period of vibration of the structures match with the dominant period of the ground (Ts). In the design of concrete structural walls is very important classified the walls according to its slenderness in order to recognize the behavior that will govern the wall, and with it determine the detailed of the steel reinforcement that could provide the best behavior when the wall be submitted to an important earthquake.

Displacement ductility for seismic design of RC walls for low-rise housing

The paper compares and discusses displacement ductility ratios of reinforced concrete walls typically used in one- and two-story houses. Ductility is investigated by assessing response measured on 39 walls tested under shaking table excitations and quasi-static lateral loads. Variables studied were the height-to-length ratio and walls with openings, type of concrete and, steel ratio and type of web reinforcement. An equation to estimate the available ductility of a wall is proposed. Based on statistical analysis of data, values of displacement ductility capacity are recommended. Displacement ductility ratios can be used to compute both strength modification and displacement amplification factors for code-based seismic design.

Estimating floor spectra in multiple degree of freedom systems

As the desire for high performance buildings increases, it is increasingly evident that engineers require reliable methods for the estimation of seismic demands on both structural and non-structural components. To this extent, improved tools for the prediction of floor spectra would assist in the assessment of acceleration sensitive non-structural and secondary components. Recently, a new procedure was successfully developed and tested for the simplified construction of floor spectra, at various levels of elastic damping, atop single-degree-of-freedom structures. This paper extends the methodology to multi-degree-of-freedom (MDOF) supporting systems responding in the elastic range, proposing a simplified modal combination approach for floor spectra over upper storeys and accounting for the limited filtering of the ground motion input that occurs over lower storeys. The procedure is tested numerically by comparing predictions with floor spectra obtained from time-history analyses of RC wall structures of 2- to 20-storeys in height. Results demonstrate that the method performs well for MDOF systems responding in the elastic range. Future research should further develop the approach to permit the prediction of floor spectra in MDOF systems that respond in the inelastic range.

Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls. I: Theory

AbstractExisting approaches used to model the lateral load versus deformation responses of reinforced concrete walls typically assume uncoupled axial/flexural and shear responses. A novel analytical model for RC walls that captures interaction between these responses for reversed-cyclic loading conditions is described. The proposed modeling approach incorporates RC panel behavior into a two-dimensional fiber-based macroscopic model. The coupling of axial and shear responses is achieved at the macrofiber (panel) level, which further allows coupling of flexural and shear responses at the model element level. The behavior of RC panel elements under generalized, in-plane, reversed-cyclic loading conditions is described with a constitutive fixed-strut-angle panel model formulation. The sensitivity of model results to various modeling parameters is investigated and results of the sensitivity studies are presented, whereas detailed information on calibration and validation of the proposed modeling approach is pr...

Inelastic shears in ductile RC walls of mid-rise wall-frame buildings and comparison to Eurocode 8

Nonlinear response-history analyses (NLRHA) are performed for 16 five- or eight-storey prototype regular reinforced concrete wall-frame (“dual”) buildings designed to Eurocode 8 for ductility class (DC) M (Medium) or H (High), in order to evaluate the higher-mode inelastic magnification of shear forces in the walls. The percentage of the total base shear taken by the walls in the 16 buildings covers evenly a range from 37 to 90 %. The NLRHA results show that there is indeed post-elastic amplification of wall shear forces due to higher modes, but that it is overestimated by the current approach for DC H in Eurocode 8. A recently proposed rational modification of that approach, which suits better modal response spectrum analysis (MRSA), is also evaluated; it is found to be in better overall agreement with NLRHA in an analysis context, but, in general, to underestimate inelastic shears above the ground storey in a design context. The design envelope of wall shears in “dual” buildings prescribed in Eurocode 8 is found to cover such shortfalls; it should be extended to wall systems as well, even in case the current approach in Eurocode 8 is modified per the recent, more rational proposals. The current design envelope of wall moments in Eurocode 8 does not safeguard against plastic hinging at upper levels; even if the linear design envelope is anchored to the moment resistance of the base section, instead of the moment from elastic analysis with the design (i.e., reduced) spectrum, it does not preclude flexural plastic hinging in upper storeys. Although for the design of walls safe-sided envelopes and approximations may be appropriate, for the purposes of evaluation of seismic performance and vulnerability of walls, NLRHA seems to be the only means to estimate with certain confidence the post-elastic higher mode effects on wall shears.

SEISMIC PERFORMANCE STUDY ON RC WALL BUILDINGS FROM PUSHOVER ANALYSIS

Buildings built completely with RC walls without frame elements are fast gaining popularity especially in urban areas. Advance in formwork technologies have made RC wall buildings an obvious choice for mass constructions because of their economy and speed of construction. Seismic performance of RC walled buildings is of primary concern in the analysis and design of such structures. Modeling of RC walls using layered shell elements has made it possible to accurately model the reinforcement configurations in RC walls and to capture the nonlinear behavior of walls efficiently. With the help of suitable nonlinear material models for concrete and reinforcing steel, pushover analysis can be conveniently adopted to assess the seismic performance RC walled buildings. In the present study, RC walls are modeled and analyzed using SAP 2000’s pushover analysis capability on layered shell elements. Various parameters such as aspect ratio of walls, reinforcement detailing aspects and presence of openings are chosen to study the seismic performance of RC walled buildings. Results of analysis have revealed that incorporation of ductile detailing in the form of boundary element significantly improves the seismic performance of RC walls specially the displacement ductility of the wall and the effects are more pronounced when the bottom storeys are strengthened with boundary elements. Presence of openings in RC walls significantly reduces base shear carrying capacity in the presence of boundary elements while it reduces both base shear capacity and ductility in the absence of boundary elements. Decrease in the aspect ratio of the wall reduces the base shear capacity of the wall while deformation capacities remain unaffected.

A STUDY OF SEISMIC POUNDING BETWEEN ADJACENT BUILDINGS

Seismic pounding between adjacent buildings can cause severe damage to the structures under earthquakes, when owing to their different dynamic characteristics. During earthquake, the buildings vibrate out of phase and at rest separation is deficient to accommodate their relative motions. Such buildings are usually separated by expansion joint which is insufficient to provide the lateral movements of the buildings during earthquakes. It can be prevented by providing safe separation distances, sometimes getting of required safe separations is not possible in metropolitan areas due to high land value and limited availability of land space. If building separations is found to be deficient to prevent pounding, then there should be some secure and cost effective methods to prevent structural pounding between adjacent buildings. There are many buildings which are constructed very nearly to one another in Metropolitan cities, because everyone wants to construct up to their property line due to high cost of land. This study covers the prevention techniques of pounding between adjacent buildings due to earthquakes. Constructing new RC walls, cross bracing system and combined RC wall & bracing, with proper placement are proposed as possible prevention techniques for pounding between adjacent buildings

Influence of the concrete DIF model on the numerical predictions of RC wall responses to blast loadings

Reliable prediction of structural responses to blast loadings requires an accurate dynamic material model. The dynamic strength of concrete material is normally higher than the static strength. Based on extensive experimental data, a number of empirical DIF (dynamic increase factor) relations have been proposed to model concrete material strength increment at high strain rates. Most of these empirical relations are obtained by fitting the scattered dynamic testing data. It is commonly acknowledged that the induced structural effects such as lateral inertia confinement effect are inevitable in high-speed impact tests. Therefore directly fitting the laboratory testing data may not necessarily obtain the true dynamic concrete material properties. Some recent studies investigated the contributions of lateral inertia and end friction confinement effects on DIF of concrete materials in laboratory tests, and proposed relations to remove these influences to obtain the true DIF for concrete materials. The present study carries out numerical simulations of a reinforced concrete wall under different blast loadings. Different DIF relations including CEB defined DIF, DIF proposed in previous studies after removing structural effect in laboratory tests, and NO DIF, i.e., neglecting dynamic strength increment, are considered in numerical simulations. Verification of the numerical model is made through the comparisons of the numerical simulation results with field test data. The results demonstrate that using the new DIF model yields the best prediction of the structural responses. The responses of a typical RC wall under blast loads with a 5m stand-off distance but different TNT explosive charge weights are also simulated using different DIF relations. The responses of RC wall obtained from numerical models with different DIF relations of concrete material are compared. From the numerical simulation results, the range of scaled distance that DIF relation has significant influences on the numerical simulation results is identified.

Special Issue on Computational Simulation in Structural Engineering

Special Issue on Computational Simulation in Structural Engineering

Capacity Design of Coupled RC Walls

Capacity design aims to ensure controlled ductile response of structures when subjected to earthquakes. This article investigates the performance of existing capacity design equations for reinforced concrete coupled walls and then proposes a new simplified capacity design method based on state-of-the-art knowledge. The new method is verified through a case study in which a set of 15 coupled walls are subject to nonlinear time-history analyses. The article includes examination of the maximum shear force in individual walls in relation to the total maximum shear force in the coupled wall system, and subsequently provides recommendations for design.

Application of air cooled pipes for reduction of early age cracking risk in a massive RC wall

The construction of massive concrete structures is often conditioned by the necessity of phasing casting operations in order to avoid excessive heat accumulation due to cement hydration. To accelerate construction and allow larger casting stages (usually increasing lift height), it is usual to adopt internal cooling strategies based on embedding water pipes into concrete, through which water is circulated to minimize temperature development. The present paper reports the use of horizontally placed ventilated prestressing ducts embedded in a massive concrete wall for the same purpose, in line with a preliminary Swedish proposal made in the 1990s. The application herein reported is a holistic approach to the problem under study, encompassing extensive laboratory characterization of the materials (including a technique developed for continuous monitoring of concrete E-modulus since casting), in situ monitoring of temperatures and strains, and 3D thermo-mechanical simulation using the finite element method. Based on the monitored/simulated results, it is concluded that the air-cooling system is feasible and can effectively reduce early cracking risk of concrete, provided adequate planning measures are taken.

Analysis of RC walls with a mixed formulation frame finite element

This paper presents a mixed formulation frame element with the assumptions of the Timoshenko shear beam theory for displacement field and that accounts for interaction between shear and normal stress at material level. Nonlinear response of the element is obtained by integration of section response, which in turn is obtained by integration of material response. Satisfaction of transverse equilibrium equations at section includes the interaction between concrete and transverse reinforcing steel. A 3d plastic damage model is implemented to describe the hysteretic behavior of concrete. Comparisons with available experimental data on RC structural walls confirm the accuracy of proposed method.

NEW STRUCTURAL SYSTEM FOR EARTHQUAKE RESILIENT DESIGN

The concept of self-centering structure and replaceable structural member or fuse is a new approach of earthquake resilient structural design. The new structural system is not only capable of preventing from failure of the structure and life safety of the occupants during earthquakes, but also quickly restoring its basic function in a short time following earthquakes. Restoring the original position through self-weight or pre-stressing forces, this kind of structures is defined as a rocking or self-centering structure. The replaceable elements of the other new kind of structural system, which includes coupling beams, energy dissipation devices, and rubber bearings and so on, are designed to be inelastic or failure, like a fuse, and to protect the main structure from damage in the region of high seismicity. The authors of this paper will report three different tests on new earthquake resilient structures, which are shaking table tests on a self-centering RC frame, quasi-static cyclic tests on RC wall with replaceable coupling beams and the ones with replaceable foot parts. All of the three new kind structural systems present an efficient resilient ability under severe horizontal forces in the tests.

Cyclic loading test for emulative precast concrete walls with partially reduced rebar section

In conventional precast concrete (PC) walls subject to cyclic loading, the ductility and energy dissipation capacity are decreased by gap opening and shear slip at the panel joints. In this study, to enhance the earthquake resistance of emulative PC walls, two potential methods were studied. First, bonded or unbonded longitudinal rebars with partially reduced cross-sectional area were used at the plastic hinge zone. By using the reduced rebar area, the PC panel at the wall bottom was weakened to develop a plastic hinge zone in the PC panel rather than at the panel joints. Second, a RC–PC hybrid wall was considered, where cast-in-place concrete was used for the plastic hinge zone at the bottom of wall. Four specimens, including an ordinary RC wall, were tested under cyclic loading. The test results revealed that gap opening and shear slip at the panel joints were prevented by using the proposed methods. As a result, the ductility and energy dissipation of the proposed PC walls were comparable to those of the RC wall.

Flexural behavior of PVC stay-in-place formed RC walls

The study experimentally investigates the flexural behavior of concrete wall strips encased with PVC stay-in-place (SIP) concrete forming system. The system consists of interconnected Polyvinyl chloride (PVC) elements; panels, connectors and bracings. Thirty PVC encased wall specimens were cast with dimensions: 457mm wide by 200mm or 250mm deep by 3050mm long. The variables studied were: the concrete core thickness (200mm or 250mm), the reinforcement ratio, and the connector type (middle and braced connector). The connectors used were middle connectors with flat panels or connectors with inclined bracing on the compression side and insulation (foam) on the tension side. All the specimens were tested under four point bending with a shear span of 1150mm. The test results showed that the PVC stay-in-place formwork system was effective in enhancing the flexural behavior of the encased walls. For a given reinforcement, the PVC encased specimens cracked and failed in the same mode, regardless of the connector type or the concrete core’s thickness. The PVC encased walls exhibited higher yield and ultimate loads in comparison to control walls. The increase in load for the PVC encased walls decreased with higher reinforcement ratios. The contribution of the PVC stay-in-place system to the ultimate load increased as the concrete core thickness decreased and/or as the reinforcement ratio decreased. A model based on strain compatibility was developed to predict the flexural capacity of PVC stay-in-place encased walls. Predictions were in close agreement with measured results.

Failure analysis of RC shear walls with staggered openings under seismic loads

Reinforced concrete shear walls are used to design buildings located in seismic areas, because of their rigidity, bearing capacity and high ductility. Until now many theoretical and experimental tests on shear walls with or without openings have been made, therefore their failure modes have been analysed and are rather very well-known; the research results being confirmed by real failure modes of RC walls after earthquakes.Design codes and standards based on the knowledge of the failure modes of the reinforced concrete walls were developed in order to obtain the ductile failure mechanisms.A special case is the failure mode of the reinforced concrete shear walls with vertical staggered openings. If at coupled walls the elements must be designed so that the plastic hinges appear at the ends of the coupled beams and then in the pier, this thing is more difficult at shear walls with staggered openings.Theoretical and experimental studies on structural walls with staggered openings, lamellar walls and walls with bulbs at the end have been made recently. There have also been studied the followings: the degradation of the stiffness, the ductility function to the intensity of the seismic force, the presence of the vertical forces, the position and the size of the openings and the reinforcing ways.The article presents the results of the theoretical and experimental tests on failure modes of three types of reinforced concrete shear walls with staggered openings which are compared to those obtained from walls with vertical ordered openings as far as the seismic response is concerned.The failure modes of the structural walls under seismic stress have been identified using calculus programs and cyclic alternated experimental tests.The theoretical research on the failure modes was the basis for the elaboration of a simplified methodology for the calculus of the maximum theoretical seismic force that produces the concrete crushing in the ultimate limit stage. The results theoretically obtained with the help of the calculus programs have been confirmed experimentally. The analysis of the failure modes, obtained with the computing methodology proposed, contributed to the completion of the seismic design codes for shear walls with staggered openings.