Medium-rise Structures Research Articles

A Review on Analysis of Seismic Impact of Improvements with Rigid and Semi Rigid RC Structure with having Podium

Abstract: The growing population and limited land in urban areas are driving up demand for towering buildings on a daily basis. India and other emerging countries are seeing an increase in the use of tall buildings. Land becomes unavailable for further expansion in any city, particularly in major cities, beyond a certain point of horizontal development. Consequently, multi-story skyscrapers gained popularity as a means of optimising land use. The design principles used for low- and mediumrise structures are not applicable to high-rise skyscrapers. Tall structures demand the most advanced design techniques since they are intricate engineering tasks. Architects and engineers proposed/put forward the new idea of Podium sort constructions in order to meet the demands of both the growing population and the present bye-laws requiring a minimum parking space for such types of buildings. These days, tower-podium style structures are quite common since they provide for the best possible use of available space on the property and the financial leverage to meet the need for more commercial space. A portion of a structure known as a podium has lateral load resistance greater than that of a tower.

Seismic performance of soil–tunnel–building systems in stiff soils

In order to study seismic soil–tunnel–building interaction in stiff soils, a metro station currently under construction, located near by a 5-story masonry building, was selected as a test site for seismic instrumentation. The site is in Mexico City, in the so-called hill zone, where very cemented sandy silt and silty sands can be found. An arrangement of five accelerometers were deployed, to assess free-field, near-field, and building seismic response. This article presents the results gathered from the seismic instrumentation after recording five low- to high-magnitude earthquakes (i.e. ranging from 4.8 to 7.7 Mw) from both interface and intraplate events. The results clearly indicate that even in low- to medium-magnitude events, the presence of the tunnel leads to peak ground acceleration (PGA) amplification both in the horizontal and vertical components, ground motion incoherence, and spectral accelerations (Sa) amplification at high frequencies. Although Sa amplification is more important for intraplate and interface low- to medium-magnitude events, frequency content modification occurs regardless of the earthquake magnitude. These facts must be accounted for when designing low- to medium-rise structures underlaid or nearby underground infrastructure such as tunnels in highly populated urban areas.

Significance of P-Delta Effects in High Rise RC Structure in Various Seismic Zones

Indian codes deal with Linear static (Equivalent static method) and linear dynamic (Response Spectrum method) methods of analysis. Guidelines are also given for Non-Linear dynamic analysis (Time history analysis) for the lateral load analysis. IS codes are silent about the guidelines for geometric non-linearity in the structure. In the case of low or medium rise structures, the geometric non-linearity will not have a significant effect, but for high rise structures, geometric non-linearity becomes a major issue. In this paper a G+50 storey RC structure with vertical irregularity is considered in such a way that P-delta effect is significant and the structure is analyzed by Linear Dynamic analysis as per IS codes and P-delta effects are included and analyzed as per ASCE code. The results such as displacement, storey drift, storey shear are compared and the significance of P Delta effects in high rise structure is studied.

Fractional Differential Equation Bearing Models for Base-Isolated Buildings: Framework Development

AbstractBase isolation is a powerful technique to prevent damage in low- and medium-rise structures during an earthquake. Nowadays, the extensive use of high-damping viscoelastic (VE) materials in ...

Evaluating inelastic performance of mega-scale bracing systems in low- and medium-rise structures

In this paper, the various aspects of the seismic performance of different concentric bracing arrangements have been inelastically analyzed in a comprehensive manner. The results suggested that mega-scale bracing systems rendered more controlled performances during severe seismic events. These systems distributed the plastic hinges in much superior manners, allowing for the inelastic capacity to come into use. They reduced the target displacements due to the reduction in the natural periods of the structures. The mega-scale bracing systems also led to 25% reduction in the weight of the structures, 54% less drift ratios and 45% smaller uplift forces. The stiffness of the stories in these systems increased up to 100% and lateral displacements reduced by up to 32%.

Quasi static study on tall building based on measured dynamic wind pressure

One important issue that arrives the serviceability design of many high-rise buildings is wind-induced discomfort. The assessment of discomfort risk for the buildings occupants due to the wind action is, therefore, of primary importance. The treatment of wind loading, which is universally applied to the design of typical low to medium-rise structures, can be unacceptably conservative for the design of very tall buildings. This study presents the experimental results of evaluating wind pressure distributions on all four faces of a tall rectangular building with 1:1.5:7 ratio. The model is made up of the acrylic sheet with a geometric scale of 1:300 with plan dimension of 10 cm x 15 cm and height of 70 cm. The model is instrumented with 192 numbers of pressure taps at eight different levels were denoted as Level 1 to level 8 corresponding to the heights of z/H ratio (where H is the height of the model) are 0.10, 0.20, 0.30, 0.50, 0.70, 0.80, 0.90 and 0.95 respectively. The model is tested using a Boundary Layer Wind Tunnel (BLWT) for twelve angles (0°, 5°, 10°, 15°, 25°, 33.5°, 45°, 56.5°, 60°, 75°, 87.5° & 90°) of wind incidence under plain terrain condition. The measured pressure data have been integrated to evaluate mean pressure coefficients, drag & lift coefficients along wind direction and perpendicular to wind direction, mean moment coefficients at each of measured levels. The average pressure coefficient values on the windward face are almost comparable at all levels, while on the smooth face and side faces the lower levels have a minimum value compared to higher levels. Mean force coefficients for level 8 are always higher than all the other levels due to edge effect at top levels. The average drag coefficient values are a good agreement with code values (IS: 875 (Part3)-1987).

Evaluation of soil flexibility of the reclaimed area in Penang using the non-destructive method

Rapid development in urban area needs solutions to address scarcity of land for the development and infrastructure. Land reclamation has played an important role in the process of urban development in Malaysia especially in Penang area. However, the land reclamation usually comes along with challenges such as instability of the reclaimed platform and soil liquefaction. Furthermore, the assumption of fixed-base structure in the current building design practice is realistic only when the structure is founded on soil class B (rock). The main objective of this study was to investigate the soil classification and liquefaction potential of the reclaimed land and to study the effect of soil flexibility on low- and medium-rise structure in terms of structure drift. In this study, two areas in Penang have been used as a case study, namely Seri Tanjung Pinang (STP) and Bandar Sri Pinang (BSP). The multichannel analysis of surface wave (MASW) method was implemented to investigate the soil classification and the soil liquefaction for the two case study areas. In addition, the pushover analysis was performed in order to study the effect of soil flexibility on low- and medium-rise structures in terms of drift. Based on the shear wave velocity (Vs30) from MASW, the STP and BSP can be categorized as soil class D (stiff soil) and E (soft soil), respectively. Results also showed that the STP area has no threat to the liquefaction potential compared with BSP area. In terms of drift, it is clearly shown that the difference of flexible-base structures at STP and BSP is 6 and 19 %, respectively, and are larger than fixed-base structure.

Flexural retrofitting of RC buildings using GFRP/CFRP – A comparative study

The effectiveness of fibre reinforced polymers (FRPs) in retrofitting/repairing of the reinforced concrete (RC) components has been studied in the past to great detail. However, the seismic performance of RC structures retrofitted using FRP composites is yet to be scrutinised in terms of lateral resistance, ductility, and failure mechanism. This is of high importance if the retrofitted structures are to withstand higher seismic ground motions than they were designed for and/or pulse-type ground motions. In a comparative study, this paper reports on the results of an investigation into the flexural strengthening of RC buildings using glass/carbon fibre reinforced polymers (GFRP/CFRP). An 8-storey code-compliant RC building was considered as the case study to represent the medium-rise structures. With a slight intervention in the lateral displacement ductility and provision of the weak-beam strong-column design philosophy, the strengthening design strategy is aimed at increasing the lateral resistance. For this purpose, composite sheets are designed to be applied at the two end regions of all beams and columns on a practical flange-bonded scheme. The nonlinear pushover analysis with lumped plasticity approach was implemented in order to compare the seismic response of the original structure with the GFRP/CFRP retrofitted structures. Following validation of the adopted models, the force–deformation curves of the nonlinear plastic hinges are determined in a rigorous approach considering the material inelastic behaviour, reinforcement details, and dimensions of the members. While the nonlinear results confirm a significant increase in the lateral load carrying capacity using both composite materials, the CFRP improvement was as much as twice of the GFRP. However, the latter provides higher ductility.

Seismic response of base isolating systems with U-shaped hysteretic dampers

This paper proposes a base isolating system to reduce the seismic demands of low- or medium-rise structures and experimentally investigates its seismic response using shake-table tests. The base isolating system considered in this study consists of laminated-rubber bearings and U-shaped hysteretic (UH) dampers which are made of high toughness steel (HTS) and are machined with slotted holes to increase their deformation capacities. A base isolated 2-story specimen for shake-table tests was first designed and cyclic tests of laminated-rubber bearings and UH dampers implemented in the base isolating systems were then carried out. The component test for the laminated-rubber bearings shows typically low lateral stiffness with enough vertical stiffness to carry gravity loads. The test results for the UH dampers demonstrate that the use of HTS material and the introduction of the slotted holes details increase deformation capacities by inducing uniform stress distribution along a UH damper. Finally, shake-table tests were performed using specimens shaken with increasing ground acceleration records. The shake-table tests show that the proposed base isolating system with UH dampers limits the seismic demands of a base isolated structure by lengthening its structural period, concentrating displacement demands on the base isolating floor and adding seismic energy dissipation from the UH dampers.

An Energy-Factor Method for the Displacement-Based Seismic Design of RC Wall Structures

A number of different displacement-based design (DBD) methods have been put forward over the past decade in order to address shortcomings with current force-based design approaches. Considerable progress has been made in developing DBD procedures for a wide variety of structural typologies. However, the new displacement based design approaches are considerably more time-consuming for simple low- and medium-rise structures than quick force-based design methods such as the equivalent lateral force method. In this work, a new simplified displacement-based design approach, referred to as the energy-factor method, is described and applied to a number of case-study wall structures. The results of the method are compared with those obtained from the equivalent force-based design approach and the Direct DBD method. The performance of the method is then gauged through a series of nonlinear time-history analyses using spectrum-compatible accelerograms. The results indicate that the simple energy-factor method could offer excellent possibilities for the performance-based design of regular low- and medium-rise structures.

Seismic behavior factors of buckling-restrained braced frames

The seismic behavior of a framed structure with chevron-type buckling restrained braces was investigated and their behavior factors, such as overstrength, ductility, and response modification factors, were evaluated. Two types of structures, building frame systems and dual systems, with 4, 8, 12, and 16 stories were designed per the IBC 2003, the AISC LRFD and the AISC Seismic Provisions. Nonlinear static pushover analyses using two different loading patterns and incremental dynamic analysis using 20 earthquake records were carried out to compute behavior factors. Time history analyses were also conducted with another 20 earthquakes to obtain dynamic responses. According to the analysis results, the response modification factors turned out to be larger than what is proposed in the provision in low-rise structures, and a little smaller than the code-values in the medium-rise structures. The dual systems, even though designed with smaller seismic load, showed superior static and dynamic performances.

비정형 셀프센터링 가새골조의 비탄성 지진응답

최근 새로운 지진하중 저항시스템으로 셀프센터링(SCED) 가새 시스템이 개발되었다. 진보된 가새 시스템인 비좌굴 가새(BRB) 시스템과는 달리 큰 지진이 발생한 후 구조물의 잔류 변형을 줄이거나 없앨 수 있는 셀프센터링 능력은 SCED 가새 시스템의 장점이다. 본 논문에서는 SCED 가새와 BRB 가새 시스템의 거동에 비틀림의 영향을 조사하기 위하여 세 가지 다른 편심을 가진 3차원 구조물의 응답을 비선형 동적해석을 수행하여 비교하였다. 해석결과에 따르면 층간변위의 높이방향의 변화는 비정형성에 관계없이 SCED 가새골조의 응답이 BRB 가새골조보다 일정하였으며, 잔류 층간변위와 잔류 회전 응답은 비정형성이 증가함에 따라 감소하였다. 중층 구조물에서 SCED 가새골조의 변형집중계수(DCF)는 BRB 가새골조보다 작은 것으로 나타났다. 이것은 SCED 가새골조가 건물 높이에 따라 보다 일정하게 변형함을 의미한다. DCF의 크기에 대한 비틀림 비정형의 효과는 작았다. A self-centering energy-dissipative(SCED) bracing system has recently been developed as a new seismic force resistant bracing system. The advantage of the SCED brace system is that, unlike other comparable advanced bracing systems that dissipate energy such as the buckling restrained brace(BRB) system, it has a self-centering capability that reduces or eliminates residual building deformations after major seismic events. In order to investigate the effects of torsion on the SCED brace and BRB systems, nonlinear time history analyses were used to compare the responses of 3D model structures with three different amounts of frame eccentricity. The results of the analysis showed that the interstory drifts of SCED braced frames are more uniform than those of BRB frames, without regard to irregularity. The residual drift and residual rotation responses tended to decrease as irregularity increased. For medium-rise structures, the drift concentration factors(DCFs) for SCED systems were lower than those for BRB frames. This means that SCED-braced frames deform in a more uniform manner with respect to building height. The effect of the torsional irregularity on the magnitude of the DCFs was small.

Safe Scaled Distance for Masonry Infilled RC Frame Structures Subjected to Airblast Loads

Terrorist bombing and accidental explosion may generate extreme loading conditions on nearby structures, resulting in damage and even collapse of structures. The degree of damage to a structure depends on the capacity of the detonation and its location as well as structural conditions. Some guidelines are available to assess the safety of unstrengthened buildings to airblast loads. These guidelines are usually given in terms of the safe scaled distance between explosion center and structure, whereas the structure conditions, which also affect its performance, are not explicitly defined. The safe scaled distance is obtained primarily from field blasting tests and experiences of structure damage to blast loads. These guidelines can be used for a quick safety assessment of structures, but do not provide clear damage scenarios of the structures. In a previous paper, damages of low-rise masonry infilled reinforced concrete (RC) structures to surface explosion of different scaled distances are numerically simulated. It was found that RC frame would collapse when the scaled distance was less than 1.82 m/kg 1/3 ; and the front masonry wall would suffer excessive damage when the scaled distance was less than about 4.5 m/kg 1/3 . The present paper is an extension of the latter work. It employs a more detailed RC model with distinctive definitions of concrete and reinforcement material performance. More thorough analyses are carried out to find the correlation between the scaled distance and the damage level of low-rise and medium-rise masonry infilled RC frames. The different failure mechanisms between the low-rise and medium-rise structures to blast loads are also observed and discussed. The computer program LS-DYNA3D with user defined RC and homogenized masonry material models is used in numerical calculations. The numerical results are also compared with the safe scaled distance recommended in the United Stated Department of Defense's regulations, ASCE guidelines, and those derived in the previous paper.

Wind Loading on Tall Buildings

Simple quasi-static treatment of wind loading, which is universally applied to design of typical low to medium-rise structures, can be unacceptably conservative for design of very tall buildings. On the other hand such simple treatment can easily lead to erroneous results and under-estimations. More importantly such a simplified treatment for deriving lateral loads does not address key design issues including dynamic response (effects of resonance, acceleration, damping, structural stiffness), interference from otherstructures, wind directionality, and cross wind response, which are all important factors in wind design of tall buildings. This paper provides an outline of advanced levels of wind design, in the context of the Australian Wind Code, and illustrates the exceptional benefits it offers over simplified approaches. Wind tunnel testing, which has the potential benefits of further refinement in deriving design wind loading and its effects on tall buildings, is also emphasized.

Discussion of “Study of viscoelastic and friction damper configurations in the seismic mitigation of medium-rise structures”

Discussion of “Study of viscoelastic and friction damper configurations in the seismic mitigation of medium-rise structures”

Study of viscoelastic and friction damper configurations in the seismic mitigation of medium-rise structures

This paper presents a comprehensive study of the seismic mitigation of medium rise frame-shear wall structures using embedded dampers. Two building structures with embedded viscoelastic and friction dampers in different configurations and placed in various locations throughout the structure are subjected to five different earthquake loadings. Finite element techniques are used to model the dampers and the structures and to obtain the dynamic responses. Influence of damper type and properties, configuration, and location are investigated using time history responses. Results for tip deflection and acceleration are evaluated for a number of cases and demonstrate the feasibility of the technique for seismic mitigation of these structures for a range of excitations, even when the dominant seismic frequencies match the natural frequency of the structure. Results also provide information which can be used for optimal damper placement for seismic mitigation.

Earthquake Protection Through Seismic Isolation

The basic problem in designing earthquake-resistant low- to medium-rise structures it that their fundamental frequency of vibration is in the range of frequencies where earthquake energy is the strongest. The building, therefore, acts as an amplifier of the ground vibrations, with the floor accelerations increasing over the height of the building. The goal of the seismic design should be to reduce the accelerations in buildings to below the level of the ground accelerations. To do this the building must be flexible.the necessary flexibility can only be achieved by using base isolation at the foundation level. After a slow start the use of isolation is increasing rapidly in the United States for buildings, retrofit, bridges, and certain types of industrial structures. The concept was met initially by considerable skepticism by the structural engineering community, but is now on the leading edge of seismic design and is being selected where levels of earthquake protection beyond code minimums are required.