PERFORMANCE EVALUATION OF VISCOELASTIC AND FRICTION PASSIVE DAMPING SYSTEMS IN VIBRATION CONTROL OF TALL BUILDINGS

This paper provides a comparison of the maximum inter-story drifts and tip acceleration of both a 16 and 30 stories building each with different structural systems; hybrid R.C moment frame with shear walls and hybrid steel frame with shear walls and X bracing which are equipped by passive dampers. Each of the building models were analyzed as fully non-linear structures for variety of dampers placements and subjected to a total of 4 different earthquake excitations. Three-dimensional (3D) finite-element models have been developed in the (FE) code LUSAS to predict the effects of passive damping on the vibrating structures. The manuscript tries to presents a rational comparison for determining dynamic response of seismic-excited high-rise buildings installed with friction and viscoelastic dampers in the cut outs of shear walls in order to capture their advantages in creating efficient damping systems. The results have shown that it is possible to achieve seismic mitigation, under all earthquake excitations, for all the structures considered in this study, by using appropriate damper types suitably located within the structure

Representing capabilities of novel semi-analytical triangular plate elements

Two novel plate-bending elements are developed and investigated in this study. Elements with 13 and 15 degree-of-freedoms are named AT13 and AT15, respectively. These triangular elements are formulated in a semi-analytic way. For this aim, the basic elasticity function is employed with unknown parameters. Subsequently, the trial-and-error procedure is used to determine the unidentified constants. Besides, the achieved results are compared with those obtained by displacement-based triangular elements with the same degrees-of-freedom (TUBA13 and TUBA15). In this research, both stress and displacement responses of diverse structures are assessed. After performing extensive numerical studies, the findings clearly demonstrate the superiorities of the proposed elements

ESTIMATION OF DISPLACEMENT CAPACITY OF RECTANGULAR RC SHEAR WALLS USING EXPERIMENTAL AND ANALYTICAL DATABASE

This study is focused on the evaluation of the displacement capacity of RC shear walls using both experimental and analytical results. The first observation of the study is that few experimental results for slender RC shear walls having thicknesses larger than 150 mm are available in the literature. From the experimental database, it was observed that the mean and the median ultimate drift of squat RC shear walls is about half of that obtained for slender RC shear walls. Considering the limitation of the experimental database, the simple empirical model for the ultimate drift ratio of slender RC shear walls proposed in this study is also based on available analytical results from the literature. The model provides a good fit with the observed results and besides, due to the fact that it does not require sectional analysis of the element, it allows a rapid assessment of the displacement capacity of slender RC shear walls as a function of the seismic design code parameters. The proposed formula can be inserted in future revisions of the seismic assessment guidelines for RC structures for rapid seismic evaluation purposes

Response control of structures with friction dampers under blast loading

Introduction: This study investigates the performance of the surface blast load acting on Moment Resistance Frames (MRF)with a novel slip load friction damper. Recently the world is facing terrorist activities that lead to the damage of the structures, including commercial, industrial, and public buildings. Methods: These structures should be protected by using control devices. Friction damper is a passive damping device that absorbs maximum energy released during vibrations. Blast loads are calculated based on empirical equations. In this study, single slip and double slip load friction dampers considering the hysteresis loops are used for controlling the response of the MRFs exposed to blast loadings. Results: The four storey, eight storey, and twenty storey MRFs with surface blast responses are controlled by using single and double slip load friction dampers. The response includes displacement, accelerations, velocity, storey drift, storey drift ratio, pressure impulse curve, etc. The torsional effect with two dimensions is considered for the high-rise structure as well. Conclusion: It was concluded that using friction dampers plays a vital role in controlling the response of MRF sunder blast loadings

The influence of coupled horizontal–vertical ground excitations on the collapse margins of modern RC-MRFs

With the increasing interest in vertical ground motions, the focus of this study is to investigate the effect of concurrent horizontal–vertical excitations on the seismic response and collapse fragilities of RC buildings designed according to modern seismic codes and located near active faults. It must be stressed that only mid- to high-rise buildings are of significant concern in the context of this research. The considered structures are categorized as intermediate and special RC-MRFs and have been remodeled using distributed and lumped plasticity computational approaches in nonlinear simulation platforms, so that the utilized NL models can simulate all possible modes of deterioration. For better comparison, not only was the combined vertical and horizontal motion applied, but also a single horizontal component was considered for direct evaluation of the effect of the vertical ground motions (VGMs). At the member level, axial force variation and shear failure as the most critical brittle failure mechanisms were studied, while on the global level, adjusted collapse margin ratios (ACMRs) and mean annual frequency of collapse (λCollapse) using a new vector-valued intensity measure were investigated. Findings from the study indicate that VGMs have significant effects on both local and global structural performance and cannot be neglected

On the quantification of collapse margin of a retrofitted university building in Beirut using a probabilistic approach

The scope of this study is to investigate the feasibility and performance of several retrofitting techniques on an existing building in Beirut Arab University (BAU). The implemented retrofitting techniques were adding RC shear walls (SW) and steel bracing systems. Simulation and analysis procedures were performed in a nonlinear platform. Models are designed based on ACI 318-14 and ANSI/AISC 360-10 for concrete and steel, respectively. Non-linear time history analysis (NL-THA), non-linear static analysis (NL-SA) and collapse margin ratio are carried out to evaluate the performance of existing and retrofitted structures. Incremental dynamic analysis (IDA) curves are then generated and used to develop the seismic fragility curves. Three different strong ground motions are used in the analyses by referring to the UBC 1997 requirement. The IDA curves are compared based on five performance levels; operational phase (OP), immediate occupancy (IO), damage control (DC), life safety (LS), and collapse prevention (CP). The fragility curves and the calculated CMRs indicated that the shear wall and steel bracing systems both provide good seismic improvement and are able to achieve strengthening solution targets for an existing building system; however, the performance of RC-SW system under seismic excitation was much better. To this, RC-SW is considered as the most appropriate technique for retrofitting the main building of Beirut Arab University

Enhancing the performance of precast hybrid concrete deep beams using curved and arched designs : experimental investigations

In recent years, deep beam performance improvement has garnered significant interest, leading to several proposed solutions. This study introduces and compares two new models of hybrid concrete deep beams, aiming to outperform conventional designs. Nine experimental specimens were subjected to one-point and two-point static loadings. The specimens shared identical dimensions, with an overall span of 1700 mm, width of 180 mm, and overall depth of 450 mm. Response parameters such as cracking and failure loads, failure modes, crack propagation rates, toughness, stiffness, and ductility were evaluated. Results indicated substantial enhancements compared to the conventional hybrid model. The curved model achieved a 5 % and 12 % increase in failure load under one-point and two-point loading, respectively. The corresponding enhancements for the arched model were 13 % and 20 %. Notably, toughness improvements ranged from 32 to 39 % and 97 % under two-point loading for the curved and arched models, respectively. Ductility gains were 39 % and 45 % under two-point loading and (45–57)% and 74 % under one-point loading for the respective models. The findings highlight the potential of the curved model with reactive powder concrete-normal strength concrete (RN) composition, offering increased load-carrying capacity and the possibility of using low-strength concrete for cost and weight reduction. The arched model also demonstrated significant enhancements. Changing the loading configuration from two-point to one-point resulted in reduced capacity, but the proposed models mitigated this reduction. This study contributes valuable insights into the behaviour of precast hybrid concrete deep beams, showcasing the superior performance of the proposed curved and arched models

Development of seismic vulnerability index methodology for reinforced concrete buildings based on nonlinear parametric analyses

This paper presents a simplified method in the seismic vulnerability assessment of reinforced concrete (RC) buildings based on proposed seismic vulnerability index (SVI) methodology. The employed procedure is derived with some modifications from the Italian GNDT and the European Macro-seismic approaches. Eight parameters were modeled in three distinct vulnerability classes to estimate the vulnerability indices of RC structures. The vulnerability classes were categorized based on the earthquake resistant design (ERD) defined as; (Low, Moderate, and High)-ERDs. Nonlinear time history analysis (NL-THA) and nonlinear static analysis (NL-SA) were carried out to define the weight of each parameter in order to calculate the seismic vulnerability index in a specific intensity (PGA) of an earthquake event. Knowing that it ranges from 0 to 1 from less vulnerable to most vulnerable with respect to the seismic intensity. In addition, the engineering demand parameter (EDP) used to determine the vulnerability index as the maximum top displacement of the structure. After determining the (SVI), The mean damage states were developed to evaluate the estimated physical damage of buildings in distinct seismic intensities. • This simplified methodology helps to manage and implements strategies for the safety of the communities before earthquake takes place by investigating the vulnerability classes for each building type. • Modeling the parameters that have an influence on the structural behavior without considering the past-damages observations through an analytical approach. • Developing the seismic vulnerability index can reduce or limit the role of the rapid visual screening methods, which is based on expert opinion decisions, and depends on observations of damages caused by earthquakes, and can be a useful framework criterion in earthquake filed

The seismic vulnerability assessment methodologies : a state-of-the-art review

In the past decades, the research and development of methodologies have received considerable attention which quantified earthquake-related damages to structures. Among these, indices of seismic risk and vulnerability assessment have indeed been developed to quantify the level of damages to structural elements or the whole structural system. In this paper, a detailed investigation has been done on the developed methodologies in the field, and the findings from other works are summarized. The authors have tried to present the most common empirical and analytical methodologies in a concise manner, which would motivate researchers and practicing engineers to use it as a comprehensive guide and reference for their future works

Blast mitigation of reinforced concrete structures incorporating shear walls in modern building designs

Material science advancements have resulted in the development of high-strength concrete and steel reinforcement, allowing more efficient and stable buildings against natural and manmade disasters. Increasing security concerns and the potential threat from terrorist activities have led to the safety and resilience of structures against blast loads in modern construction. The present study investigates the performance of reinforced concrete shear walls in mitigating blast-induced vibrations. The study examines four different reinforced concrete buildings based on their shapes, namely square, rectangular, C-shaped, and L-shaped, to understand the blast behaviours with and without shear walls. The study presents a methodology to protect the regular and irregular buildings equipped with shear walls against blast loads at varying standoff distances of 100 m, 200 m, 300 m, and 400 m, respectively. The study also compares the efficiency of passive control dampers and shear walls in enhancing the buildings’ performance against blast vibrations. The best placement of the shear walls is also evaluated for all the selected buildings. The study also considers the effect of shear wall thickness in mitigating blast-induced vibrations in multi-storey buildings. The study also discusses the design guidelines and reinforcement detailing of shear walls to protect buildings against detrimental blast effects