RC Frame Buildings Research Articles

Experimental Estimation of Period of Vibration for Multistory RC Frame Buildings (Dept.C)

At the present lime most current building codes specify equations to be used for the calculation of the base shear and lateral loads. For the determination of these lateral loads, it is necessary to determine first the period of vibration of the building. As is known, the period of vibration of buildings can be determined theoretically or experimentally. The theoretical design values of the period ol' vibration are different from the experimental ones. Significant differences have been observed for RC multistory frame buildings and in a lesser degree for other building types such as: masonry, stone, large-paneled, and large-brains buildings. The natural periods of vibration of 53 multistory RC frame buildings have been measured by the station of Engineering-Seismometer Services (ESS). These 53 buildings have different number of stories, different dimensions in.plan (with different plan length to width ratios) and effected on different soil conditions. On the basis of these data an improved simple empirical equation relating the period of vibration and the number of stories of the building is proposed 113 estimate the fundamental period of vibration of RC multistory frame buildings. In this paper the effect of soil condition and the divisions of the building in plan on the period of vibration have been studied. Comparison of periods determined using the proposed relationships and the adopted ones shows rather well agreement.

Effect of Setback Irregularity Location on the Performance of RC Building Frames Under Seismic Excitation

Effect of Setback Irregularity Location on the Performance of RC Building Frames Under Seismic Excitation

Drift and Response Reduction Factor of RC Frames Designed with DDBD and FBD Approach

Performance-based seismic evaluation of 2-, 4-, 8- and 12-story RC frames designed using direct displacement-based design (DDBD) and convectional force-based design (FBD) approach as per Indian standards is carried out. The DDBD approach is implemented for the design of RC frames using IS 1893 spectrum. The capacity curve and the performance point of designed RC frames are obtained by analyzing frames using nonlinear static pushover analysis. The response reduction (R) factor of designed RC frames as per FBD and DDBD method is evaluated from the bilinear idealization of capacity curve. The designed moment resisting RC frames are analyzed using nonlinear time-history analysis (NLTHA) to investigate the damage index in the form of lateral drift profile. Comparison of the NLTHA results in terms of inter-story drift ratio (IDR) and nonlinear static analysis results in terms of performance point and the response reduction (R) factor for RC frame buildings indicates the efficiency of the DDBD approach. The values of ‘R’ factor of RC frames designed with DDBD approach are observed higher than that of similar frame designed using FBD approach, indicating higher dissipation of energy through the nonlinear behavior of DDBD frame. The result shows that the building height is a crucial parameter affecting the ‘R’ factor of RC frame. The RC frames designed with DDBD approach are observed comparatively economical as compared to designed using FBD approach. The IDR of RC frames designed with DDBD approach is observed relatively higher than that of similar frames designed with FBD approach.

Real-Time Hybrid Test Using Two-Individual Actuators to Evaluate Seismic Performance of RC Frame Model Controlled by AMD

Seismic responses of a single-story RC frame building model under control using an active mass damper (AMD) are demonstrated through a real-time hybrid simulation (RTHS) method. In this study, the RTHS test is carried out by using a hydraulic actuator and a shaking table under a synchronization. Most parts of the target RC frame model are provided as an analytical model for an online computer simulation, and the only single column of the first story is prepared as an experimental substructure. A hydraulic actuator deforms the actual RC column, and uncertainty or nonlinearity of the RC column’s behavior is focused on this RTHS test. At the same time, a control device of AMD is actually tested under a situation of installing it on the target building's floor. The floor response of the target building model is generated using a shaking table. A control motion of the AMD is manipulated based on an online simulation of the entire RC building model. Firstly, a time delay compensation of the hydraulic actuator is considered. Time delay parameters are identified using a combination model of a time lag and a first-order delay. A PID controller and a time series compensator (TSC) are applied to improve actuator performances. Next, the reproducibility of the RTHS test using two-individual actuators is evaluated. The tracking of a restoring force and deformation of the actual RC column specimen generated by the hydraulic actuator and floor motion responses reproduced on the shaking table are investigated. To improve the online numerical simulation based on the measured force responses of the RC column specimen, a high-pass filter (HPF) is applied for a force correction to utilize its phase-lead property. The effect of this HPF force correction is evaluated in both a linear region and a strong nonlinear region of the actual RC column specimen. Finally, the RTHS test results are compared to fully-numerical simulations, and the control effect of the AMD to increase the damping effect for the target RC building model is also investigated.

Seismic demand model class uncertainty in seismic loss analysis for a code-designed URM infilled RC frame building

Probabilistic seismic risk is affected by several sources of uncertainty. Investigating their influence on loss analysis results is essential to obtain reliable quantitative estimations of seismic performance. Within the framework developed by the Pacific Earthquake Engineering Research (PEER) Center for probabilistic seismic loss analysis, this study incorporates the effect of seismic demand model class uncertainty on seismic risk performance metric estimation. The extended formulation is illustrated with an application example code-designed reinforced concrete moment resisting frame building with unreinforced masonry (URM) infill walls, where model class uncertainty related to URM infill walls modeling is propagated to the estimation of seismic financial losses. Model class uncertainty accounts for the variability arising from the use of different modeling solutions, such as the ones associated with the adoption of three equivalent strut macro-models and their modeling parameters. Probabilistic distributions are assigned to selected infill strut model parameters, and a large set of finite element models (FEMs) are generated for each infill strut model class by sampling the model parameter distributions through Latin Hypercube Sampling (LHS). Expected values of repair cost and life-cycle annualized loss are evaluated and compared for two sets of three building performance models. The first set considers the original (median) values of infill strut backbone parameters, while the second set includes model parameter uncertainty. The uncertainty propagation from structural response results to repair costs is also reported for the six performance models. Finally, the contribution of different structural and non-structural element categories to the financial losses is presented.

Push Over Analysis of RC Frame Buildings with and Without Infill Wall

Push Over Analysis of RC Frame Buildings with and Without Infill Wall

Resilience-based retrofitting of existing urban RC-frame buildings using seismic isolation

The improvement of the seismic resilience of existing reinforced-concrete (RC) frame buildings, which is essential for the seismic resilience of a city, has become a critical issue. Although seismic isolation is an effective method for improving the resilient performance of such buildings, target-oriented quantitative improvements of the resilient performance of these buildings have been reported rarely. To address this gap, the seismic resilience of two existing RC frame buildings located in a high seismic intensity region of China were assessed based on the Chinese Standard for Seismic Resilience Assessment of Buildings. The critical engineering demand parameters (EDPs) affecting the seismic resilience of such buildings were identified. Subsequently, the seismic resilience of buildings retrofitted with different isolation schemes (i.e., yield ratios) were evaluated and compared, with emphasis on the relationships among yield ratios, EDPs, and levels of seismic resilience. Accordingly, to achieve the highest level of seismic resilience with respect to the Chinese standard, a yield ratio of 3% was recommended and successfully applied to the target-oriented design for the seismic-resilience improvement of an existing RC frame building. The research outcome can provide an important reference for the resilience-based retrofitting of existing RC frame buildings using seismic isolation in urban cities.

Assessment of Building Robustness against Disproportionate Collapse

This paper presents a methodology to assess the robustness of moment-resisting RC frame buildings under multiple-column-loss scenarios. In the proposed approach, kinetic and strain energy are employed as objective measures of the dynamic effects and the plastic deformations induced in buildings by the sudden loss of a bearing element, whereas a unique chord rotation is used as an explicit indicator of the global system deformation. These quantities are utilized to define a critical path index ICP that allows identifying the areas most impacted by column loss and determining the location of the next critical column in the building. The proposed index is integrated into a systematic methodology that identifies the minimum number of columns that need to be removed to induce structural collapse. An extensive numerical investigation was conducted on three-dimensional RC buildings of varying height. Comparisons between the demand induced on the buildings by the identified critical path and random column removals confirm that the sequence identified by the proposed methodology is the one that induces the most severe demands on the structure. Correlation between the variation of the system strain energy and the activation of secondary resisting mechanisms that develop as more columns are removed also confirms the ability of taller buildings to engage larger portions of the structure in resisting progressive collapse. The proposed methodology provides an objective approach for comparing the relative robustness of buildings subjected to column losses and help advance the understanding and mitigation of disproportionate collapse.

Effectiveness of Different Techniques on the Seismic Retrofitting of Existing RC Framed Buildings in Saudi Arabia

Effectiveness of Different Techniques on the Seismic Retrofitting of Existing RC Framed Buildings in Saudi Arabia

Seismic assessment of RC building frames using direct-displacement-based and force-based approaches

The conventional force-based design (FBD) method has been in practice for seismic assessment of RC building frames. In the FBD method, the main focus is on the seismic forces over the structure. In recent years, various shortcomings have been pointed out by research works, for example assumed initial stiffness of structural components, inappropriate response reduction factors, etc. To overcome these limitations of FBD, many new techniques have been developed and implemented. One such method is the direct-displacement-based design (DDBD) method. In this, the basic assumption is that strength is less critical than displacement. DDBD is a design theory in which design criteria are articulated for achieving a specified level of performance goals that are subjected to the defined level of seismic hazards. In this paper, the vulnerability of buildings situated in high seismic regions in India has been assessed. Four- and eight-storey RC building frames are taken into consideration. The non-linear time-history analysis is carried out, and the inelastic behaviour of buildings in the form of base shear, inter-storey drift ratio (ISDR) and maximum displacement is assessed. Also, fragility curves have been developed considering the effect of ISDR. It is concluded that the DDBD approach is more reliable and efficient for designing RC building frames as compared to its counterpart FBD approach.

Optimum energy based seismic design of friction dampers in RC structures

Friction-based dampers are considered as one of the most efficient Energy Dissipation Devices (EDDs) due to their advantages such as adjustability and high energy dissipation capacity. However, their efficiency is strongly associated with the design slip load values along the structure. Conventional design methods using uniform slip load distributions may result in concentrating and localizing damage in certain storey levels. In this study, a practical energy-based optimization methodology is developed for seismic design of RC frame buildings with friction-based EDDs. The proposed method aims at improving the seismic performance of the structure by redistributing the slip loads of friction dampers to obtain a more uniform height-wise distribution of energy dissipation capacity. This leads to a design solution with maximum energy dissipation, and therefore minimum structural damage under a design earthquake. The low computational cost and efficiency of the proposed method is demonstrated through the optimum design of 3, 5, 10, 15 and 20-storey RC frames equipped with wall-type friction dampers under a set of synthetic spectrum-compatible earthquakes. The results show that after only a few steps the optimum design frames exhibit up to 31% and 70% less maximum inter-storey drift and global damage, respectively, compared to their conventionally designed counterparts.

Natural period of reinforced concrete building frames on pile foundation considering seismic soil-structure interaction effects

The magnitude of seismic forces induced within a building, during an earthquake, depends on its natural period of vibration. The traditional approach is to assume the base of the building to be fixed for the estimation of the natural period and ignore the influence of soil-structure interaction (SSI) citing it to be beneficial. However, for buildings resting on soft soils, the soil-foundation system imparts flexibility at the base of the building and it is imperative for SSI effects to exist that may prove to be detrimental. Presence of SSI effects modifies the seismic forces induced within the building, which is dependent on the change in its fixed base natural period. Expressions for determination of the natural period of a structural system under the influence of SSI (effective natural period) are available in the literature. Although useful and made applicable to all types of foundation systems, these expressions are developed either using simplified models or are applicable to shallow foundations and may not be suitable to all types of structural-foundation systems in general. This article investigates the influence of seismic soil-structure interaction on the natural period of RC building frame supported on pile foundations. Detailed finite element modelling of an exhaustive number of models, encompassing various parameters of the structure, soil, and the pile foundation has been carried out in OpenSEES to study the effect of SSI on the natural period of the RC building frame. The effect of various parameters on the natural period of the building frame under SSI is investigated and the results have been used to develop an ANN architecture model for the estimation of the effective natural period of RC building frame supported by pile foundation. Garson’s algorithm is used to conduct sensitivity analysis for examining the importance of various parameters that govern the determination of effective natural period. A predictive relationship for obtaining the effective natural period has been proposed using ANN architecture in the form of a modification factor that is to be applied on the fixed base natural period, and which depends on various input parameters of the building frame-pile-soil system. A comparison of the proposed relationship with those available in literature demonstrates its usefulness and applicability to RC building frames on pile foundations.

Effects of Sandy Soil-structure Interaction on the Natural Period of RC Building Frames

Building natural period, T, is a key character in building response for wind and seismic induced forces. In design practice, the period, T, is either estimated from empirical relations proposed by the design codes or determined from analytical or numerical models. The effect of the soil-structure interaction is usually neglected in the design practice and analysis models. This paper uses a sophisticated finite element simulation to investigate the effect of soil-structure modeling on the fundamental period of RC buildings subjected to wind and seismic induced forces. A typical interior building frame has been imitated using the frame element for beams and columns with constrains to model the almost-rigid diaphragm nature for floors and roof while a three-dimensional element has been adopted for the raft foundation and the soil mass. Different sandy soils have been considered. Standard Penetration Test, SPT value, has been taken as an identification index for soil nature. All other soil properties have been estimated based on well-accepted correlations. After applying the gravity dead and live loads, and eigenanalysis has been achieved to show how soil flexibility affects the effective stiffness of the structure and the corresponding natural period. Finally, the results are used to introduce a correction factor to modify the natural period estimated from a linear analysis with ideal supports to reflect the aforementioned effects.

Investigating the efficiency of DDBD approaches for RC buildings

Direct displacement-based design (DDBD) approach attempts to alleviate the shortcomings of force-based design (FBD) approach to achieve seismic resistance of structures. Many simplified procedures for DDBD proposed in the literature are conceptually similar, yet differ in their considerations for crucial parameters such as target displacement profile, equivalent viscous damping equation and base shear distribution pattern in the design process. Due to variation in the aforementioned parameters, seismic force, their distribution and element design differs, leading to significant changes in the inelastic behavior of the building. The present numerical study compares the performance of low, medium and high-rise RC frame buildings designed using six DDBD approaches for two drift levels. The seismic performance of the considered buildings has been deliberated by both nonlinear static pushover as well as nonlinear dynamic time-history methods. From analysis results, it is observed that the 84th percentile of the sample mean storey displacement of low-rise buildings designed for low storey drift exceeds the target profile, whereas, this behavior is contrary in high-rise buildings designed for higher storey drift. The analysis also highlighted that the parabolic displacement profile consideration for mid and high-rise buildings is rational than the linear displacement profile consideration. In the present case, it seems that equivalent viscous damping estimation and displacement spectra modification factors are conservative for all the DDBD approaches and needs modification to improve its rationality.

Seismic performance of RC frame buildings accounting for the out-of-plane behavior of masonry infills

Past earthquakes have repeatedly shown that damage to masonry infills can produce large economic losses and even jeopardize human lives. Nevertheless, in current design practice masonry infills are ignored, while available macro-models for nonlinear analysis focus the attention on the In-Plane (IP) behavior of masonry infills only, while neglecting the Out-Of-Plane (OOP) collapse mechanism. The main objective of this study is to investigate the seismic performance of RC frame buildings accounting for the interaction between IP and OOP behavior of masonry infills. To this end, a suitable nonlinear model, able to capture the IP stiffness and strength reduction due to the OOP displacement demand (and vice versa) is implemented. The selected model incorporates a routine that removes infills from the structural model when either IP or OOP collapse occurs. Different building models, representative of typical residential buildings, realized in Italy (and other European countries) from 50’s to 90’s, are examined through nonlinear response-time history analysis at different earthquake intensity levels, with return period ranging from 30 to 5000 years. Two alternative infill configurations (single layer and double layer with inner cavity) are considered, in accordance with the construction practice of the time. The comparison between the models with and without IP/OOP interaction points out the relevance of the OOP behavior towards an accurate evaluation of the seismic performance of RC frame buildings. A set of fragility curves is tentatively proposed, for different building performance levels, ranging from immediate occupancy to life safety.

Use of Conditional Mean Spectra for Seismic Evaluation of RC Building Considering Soil Effects

Recently, the conditional mean spectrum (CMS) has become an important tool in ground-motion selection for seismic evaluation of structures. In the present numerical study, a 10-storey RC frame building is assumed to be situated on type-II soil and located in seismic zone V of India. The building is designed using the response spectrum analysis method of the Indian seismic code. Further, it is analysed using the nonlinear time history analysis method for three different CMS ground motions. The numerical study is performed for three cases: (1) fixed base with actual earthquake record; (2) fixed base with site-specific earthquake record considering soil amplification; and (3) flexible base considering soil–foundation flexibility and soil amplification. The results of the analysis are compared for the above-mentioned cases in terms of lateral displacement and storey drifts. It is observed that the displacement profile of the structure subjected to all the three considered ground motions is not the same, although they are matching to CMS. It is concluded that out of the two important soil effects, i.e. soil amplification and soil–foundation flexibility, soil amplification has a significant effect on the seismic response; however, the nature of response depends mainly on the ground-motion characteristics.

The effect of finite element modeling assumptions on collapse capacity of an RC frame building

The main objective of seismic codes is to prevent structural collapse and ensure life safety. Collapse probability of a structure is usually assessed by making a series of analytical model assumptions. This paper investigates the effect of finite element modeling (FEM) assumptions on the estimated collapse capacity of a reinforced concrete (RC) frame building and points out the modeling limitations. Widely used element formulations and hysteresis models are considered in the analysis. A full-scale, three-story RC frame building was utilized as the experimental model. Alternative finite element models are established by adopting a range of different modeling strategies. Using each model, the collapse capacity of the structure is evaluated via Incremental Dynamic Analysis (IDA). Results indicate that the analytically estimated collapse capacities are significantly sensitive to the utilized modeling approaches. Furthermore, results also show that models that represent stiffness degradation lead to a better correlation between the actual and analytical responses. Results of this study are expected to be useful for in developing proper models for assessing the collapse probability of RC frame structures

Comparative Study on Seismic Behaviour of RC Frame Building with and without Staircase

Comparative Study on Seismic Behaviour of RC Frame Building with and without Staircase

Assessment of Serviceability Fluctuation of RC Frame Building for Similar Type of Soil Based on Bangladesh National Building Codes (BNBC)

Assessment of Serviceability Fluctuation of RC Frame Building for Similar Type of Soil Based on Bangladesh National Building Codes (BNBC)

Experimental Testing of Variable Stiffness Bracing System for Reinforced Concrete Structure under Dynamic Load

ABSTRACT This study reports the development of variable stiffness bracing (VSB) system as the lateral resisting element for RC-framed structures subjected to dynamic load. This device can enhance the lateral stability of structures against dynamic loading. The developed VSB device includes a nonlinear leaf spring, which provides variable stiffness characteristics to the system and can be considered a passive structural control system because it is independent of any external power source. A new design for the VSB of structures is proposed, and a prototype is fabricated and installed in an RC frame subjected to dynamic experimental tests. The effect of VSB implementation in an RC frame under dynamic loading is evaluated and compared with a bare frame. Furthermore, the numerical study includes pushover and time history analyses to assess the seismic performance of the developed VSB device. The results of the experimental test and numerical simulation confirmed the efficiency of the developed VSB device as a resisting/retrofitting technique for RC-framed structures. The ductility trend, overall stiffness, and final capacity of the frame improved when the VSB was implemented in the frame. Given that the VSB device can be simply fabricated and installed in an RC frame, the VSB device can also be used as an alternative for increased lateral stability and energy dissipation tendency in new RC-framed buildings. Furthermore, this device can be used as a rapid retrofitting strategy for existing RC buildings.