Bare Frame Research Articles

Strengthening of existing RC buildings by using autoclaved aerated concrete infill wall

ABSTRACT The objective of this study is to use autoclaved aerated concrete (AAC) for infill walls in existing buildings that are unsafe for earthquakes to increase their stiffness. The study included two topics; the first topic introduced six models using AAC in buildings resistance to earthquakes and the effect of self-weight of the buildings comparing bare frame clay partition masonry model (1), bare frame AAC partition masonry model (2), reinforced concrete frames clay infill wall model (3), reinforcement concrete frames AAC infill wall model (4), reinforcement concrete frames AAC infill wall core model (5), reinforcement concrete frames AAC infill wall first and second floors model (6). ETABS software was used to investigate all frame models. Results of the study revealed that AAC infill wall decreases base moment, base shear and displacement. On the other hand, second topic presented five models of single reinforcement concrete frame under lateral loading, considering effect of anchored and unanchored AAC infill wall and clay infill wall. These models are bare frame model (a), RC frame with clay infill wall unanchored model (b), RC frame with AAC infill wall unanchored model (c), RC frame with clay infill wall with anchors model (d), RC frame with AAC infill wall with anchors model (e). Using finite element software (ANSYS WORKBENCH 18.2) failure load, displacement and ductility were presented for all five frames. The results showed that the ‘RC frame with AAC infill wall with anchors’ model gives the biggest failure load whereas displacement and ductility are the lowest.

Analysis of a building under composite structural system: A review

A composite structural system or dual structural system is a structural system in which a whole frame provides strength for gravity load and moment-resisting frame or bracings provide support for lateral loadings. The objective of the study is to review the distinctive lateral load resisting system that is being used for lateral strength but still not entirely satisfied with the enactment of the structure under the dynamic response of a building. For the contemplation of dynamic nature, the important parameters like Base shear, Base moment, Storey shear, story displacement, and relative displacement are taken into consideration and for time period analysis parameters like the total height of the building, story height, stiffness, mass and number of storeys is taken into consideration and are reviewed from the literature and their effect in both linear and non-linear dynamic states are studied. The paper contemplated the response of building against lateral load and a comparative response is studied between the bare frame and frame with the shear wall, bracings, and other probable measures embracing distinctive structural configurations is carried out and the results are conferred taking different steel sections, and bracings pattern. The paper also focused on the effect of ground motion acceleration of different magnitude incorporating with distinctive non-linear dynamic parameters specifically the effect of variation in Peak Ground Acceleration on roof displacement, roof acceleration and base shear in different directions and studied that it’s not necessary peak PGA results in peak response of roof drift, displacement, base shear and acceleration.

Effect of Lead Rubber Bearing on Seismic Response of Regular and Irregular Frames in Elevation

Base isolations are acknowledged as an effective seismic protective system for structural systems of buildings. This study investigates the effectiveness of lead rubber bearing (LRB) on the nonlinear response of the steel moment resisting frames subjected to real ground motions. To this aim, 12-storey regular and irregular steel frames in elevation upgraded with LRB were studied by evaluating the local and global deformations. LRB was modeled by considering three key parameters of isolation period, effective damping ratio, and stiffness ratio. Two-dimensional model of the base isolated frames were created and a series of time-history analyses were carried out by different earthquake ground motions. The seismic behaviour of the bare and isolated frames was measured by the variation of isolator displacement, acceleration, interstorey drift ratio, relative displacement, roof drift ratio, normalized base shear, base moment, and hysteretic curve. The supremacy of the base-isolated frames over the bare frames was discussed accordingly. It was found that the seismic response of the regular and irregular frames in elevation could be improved up to a certain degree by implementing LRB.

Numerička analiza armiranobetonskih okvirnih zgrada sa izolovanom zidanom ispunom

Reinforced concrete (RC) buildings with masonry infill walls are widely used in many countries all over the world. Although infills are considered as non-structural elements, they significantly change dynamic characteristics of RC frame structures during earthquake excitation. Recently, significant effort was spent on studying decoupled infills, which are isolated from the surrounding frame usually by adding a gap between frame and infill. In this case, the frame deformation does not activate infill wall, thus infills are not influencing the behaviour of the frame. This paper presents the results of the investigation of the behaviour of RC frame buildings with the INODIS system that decouples masonry infills from the surrounding frame. Effect of masonry infill decoupling was investigated first on the one-bay one-storey frame. This was used as a base for parametric study on the frames with more bays and storeys, as well as on the building level. Change of stiffness and dynamic characteristics was analysed as well as response under earthquake loading. Comparison with the bare frame and traditionally infilled frame was performed. The results show that behaviour of the decoupled infilled frames is similar to the bare frame, whereas behaviour of frames with traditional infills is significantly different and demands complex numerical models. This means that if adequate decoupling is applied, design of infilled frame buildings can be significantly simplified.

Seismic Fragility Curves for RC Flat Slab Buildings with and Without Infill

Rapid urbanization leads to more demand for construction of commercial buildings in Indian cities. The ease construction and more space demand of buildings are constrained in conventional buildings. To overcome constrained, the flat slab buildings evolved and practiced recent time in urban cities. It is becoming more popular for multistoried commercial buildings but experiences larger displacements under lateral load effect caused by earthquakes. These buildings need urgent to assess the vulnerability of buildings. In this fragility analysis is carried out, and it is useful for the evaluation of the probability of structural damage due to earthquakes as a function of ground motion indices. This paper is an attempt made to develop the fragility curves for seven-storey RC commercial buildings and a comparison made between the bare frame, flat slab, flat slab with drop, flat slab with drop and perimeter beam buildings without and with exterior infill walls. The building models are analyzed using ETABS software and designed as per IS 456. In this, infills are considered along the perimeter of the plan of the building and no infill in ground storey. The infill wall is modelled as equivalent diagonal strut model. The Auto hinges are assigned for both beam and column members. Pushover analysis has been performed on the building models using ETABS software. Yield and ultimate spectral displacement and spectral acceleration are obtained from capacity curves. For the development of fragility curves, HAZUS methodology has been used. Fragility curves are developed for all the eight building models and compared the probability of damage of structures for bare frames and open ground storey buildings. In this assumed, the expected intensity ground motion is considered as seismic zone PGA values. It is observed that in considered flat slab models, flat slab with drop and perimeter beam building is showing minimum probability of damage results in both with and without infill for given intensities.

Effect of Steel Bracing in Progressive Collapse of Multi Storey RC Buildings

Rapid increase in manmade and natural disasters can lead to structural instability which triggers the partial or complete collapse of the building. These manmade disasters include gas cylinder explosion or terrorist attack or instant removal of the primary structural element which leads to the progressive collapse of the building. To avoid the progressive collapse of building due to man-made disasters, incorporate the mechanism which resists the man-made disaster while the design for existing or newly constructing building. In this paper, an attempt is made to understand the effect of with and without providing steel bracing at various positions column removal in multi-storey building one at a time as per General Service Administration and Unified facilities criteria codes. The propagation of progressive collapse with and without the effect of steel bracing is studied in this paper. A seven-storey RC building is modelled and analysed for various column removal scenarios in SAP 2000 software. The Loads are applied according to General Service administration and Unified facilities criteria guidelines, column removal positions namely centre, edge and corner column removal at ground floor are also considered from guidelines. The three scenarios are then analysed individually as a bare frame, bare frame with steel bracing in the wall and bare frame with steel bracing in the slab. Push down analysis is carried out on models and results of mode shapes, time periods, force Vs displacement curves, plastic hinge deformation are discussed. From results, it is observed that wall bracings have better performance in all three and can help in arresting the progressive collapse from spreading throughout the building.

Effect of Infill Wall on Vertical Irregular Tall Structure

In reinforced concrete (RC) frames, the masonry infill walls are used to fill the gaps between the two columns and one horizontal beam which form the single bay. Stiffness of this bay or reinforced concrete frame structure increases by filling the gap between the bays of a structure. The present study investigates that the influence of the infill wall in the vertical irregular tall structure with bottom soft storey and the behavior of (G+14) storey building subjected to seismic load. The study carries different type of models which are regular frame, regular full infilled frame, regular infilled with 15% central opening frame and regular infilled with 15% corner opening frame are analysed. Similarly the same study has been extended for vertical irregular bare frame, inverted vertical irregular bare frame. This study is made for a case applicable to earthquake zone (III), soil type (II) with importance factor (1) and M20 grade of concrete. The analysis is performed using the equivalent static method and response spectrum method as per IS 1893-2016 using E-Tabs 2015 commercially available software. The parameters considered for study are storey displacement, storey drift and base shear. The results obtained for storey displacement and storey drift, in the infilled frame are reduced due to presence of infill wall. However, as expected, the base shear is increased from bare frame to infilled frame.

Progressive Collapse Analysis of Three Dimensional Two Bay Five Storey Bare and Infilled Frames under Corner and Middle Column Removal

Demand Capacity Ratio (DCR) assessment of the structural progressive collapse of two bay five storey bare frame without wall load , bare frame with wall load and Infilled frame with cement mortar (IFCM). IN this paper linear static analysis is carried out under corner and middle column removal base on GSA guidelines. Finite element software was used to design two bay five storey reinforced concrete building frame using Indian Standard (IS code). Finally all the three cases according to the progressive collapse resistant behaviour indicator DCR values to investigate in ability in progressive collapse, this present result shows Infilled frame with cement mortar shows to prevent the progressive collapse of Reinforced concrete building.

Response of laminated glass-CLT structural components to reverse-cyclic lateral loading

Innovative hybrid structural components composed of cross-laminated timber frame and laminated glass infill were tested to examine their response on the reverse-cyclic loading. Ductile timber-frame joints with glued-in steel rods and especially designed glass-to-timber contacts with no adhesive proved to provide high ductility and energy dissipation of structural components. In total, 20 tests of full-scale specimens were carried out; three bare frames, six frames with single glazing and eleven frames with double glazing. Deformation capacity, lateral strength, stiffness and strength deterioration and energy dissipation capacity were analysed in order to provide data for the future development of computational models and design guidance for the new codes.

Behaviour of steel frames infilled with environmentally and structurally favourable masonry units

The interaction of a steel frame and its masonry infill under horizontal loads has both beneficial and detrimental aspects, both complex to encompass in design guidelines due to a large number of variables. There are various approaches to this problem, among which a popular research theme in steel is the omission of infill influence on the steel frame, to prevent detrimental effects. With this in mind, our previous research was devoted to the development of environmentally and structurally favourable masonry units, which would magnify beneficial aspects of steel-frame interaction and alleviate negative aspects. This research was a continuation of such efforts in the form of cyclic testing of steel frames infilled with newly developed masonry units. An experimental investigation on four various types of steel frame and infill and a bare frame was executed, i.e. various configurations of frame-infill systems were tested under cyclic load. The structural behaviour properties of these configurations are studied and evaluated based on obtained hysteresis loops and their envelopes – ductility, initial stiffness, and ultimate load. In comparison with previous research results on frame infill configurations with different kinds of infill, promising results obtained in the development of masonry units were verified. Frame infilled with new units has high ductility and robustness, combined with lower initial stiffness. This ensured the preservation of the frame from stronger detrimental effects, with enchantments of positive aspects of the frame-infill interaction.

Probabilistic estimation of floor response spectra in masonry infilled reinforced concrete building portfolio

The seismic performance of non-structural elements is now recognized to be a key issue in the seismic assessment and earthquake related loss estimation of buildings, both at the individual and regional scale. The evaluation of the seismic demand on non-structural elements in many modern building codes is often based on inaccurate distributions of floor accelerations. For this reason, some design oriented simplified methodologies have been developed recently to predict floor response spectra in reinforced concrete buildings. Although the influence of masonry infills on the seismic performance of reinforced concrete buildings has been widely demonstrated, infills are generally neglected both in the design and in the evaluation of floor response spectra, which could lead to un-conservative design of non-structural elements. In this paper, the effect of masonry infills on absolute acceleration and relative displacement floor response spectra for reinforced concrete buildings subjected to frequent (serviceability level) earthquakes is investigated through a probabilistic framework. A database of one hundred masonry infilled reinforced concrete frames, representative of the European context, was generated and each building analyzed through nonlinear time history analyses. From the results of these analyses, the acceleration and displacement response spectra at different floor levels of both bare and infilled frame archetypes were then computed. The effectiveness of the most common assumptions made in regional risk models to estimate the non-structural losses is investigated and a first attempt at a more refined approach taking into account the effect of masonry infills is proposed.

Performance of RC Asymmetrical Building With and Without Bracings by Linear Static and Time History Research

In asymmetrical Reinforce concrete (RC) buildings, the most effective and practical method of enhancing the seismic resistance and to reduce lateral displacement of the structures by combining bracings elements in the frame. Although past studies have focussed on the modelling of bracing elements, symmetric building models in linear analysis, there have been no detailed investigation on asymmetric structures under seismic excitation. Inclined elements (bracings) react as truss web elements which would bear compression or tension stresses. In present study a G+5 symmetrical RC bare frame, asymmetrical RC bare frame, asymmetrical RC frame incurred with different types of bracings such as X, V, inverted V, eccentric forward, eccentric back bracings at outer positions in all floors. Structural members of G+5 frame are designed as per the provisions of Indian seismic code IS: 1893 (Part-1)-2015. It was observed that maximum reduction both in X direction and Y-direction for x-type bracings in all models. It was observed that the maximum storey drift ratio of the structure under permissible limits as per the Indian seismic code IS: 1893 (Part-1)-2015 from linear static and dynamic analysis. From results obtained from linear static and dynamic analysis, the maximum forces in beams and columns reduced significantly X bracings in symmetric plan and asymmetric plan model

Performance of Outrigger System by Non-Linear Static Method

High rise building structures are highly affected by lateral loads and wind forces. To enhance lateral force outrigger systems are developed, which are one of the most popular and efficient, because they are easier to build and they provides good lateral stiffness. With the rise of building height, deep beam become concrete walls at least of one story height. Axial shortening effect between core and perimeter structure has to be considered.In the present work 20 story reinforced concrete structure has taken with outrigger walls attached from core to the outer perimeter column. By changing the different position of outrigger level are kept for analysis.The building without and with outrigger are compared with bareframe. These are different building models analysed (a) Bare frame of twenty story building (b) Bare frame with core shear wall building (c) Outrigger system at top of building (d) Outrigger system at top & 0.75 Height of building (e) Outrigger system at top & 0.50 Height of building (f) Outrigger system at top & 0.25 Height of building. Non-linear static analysis results were compared. The analytical methods used in the work are pushover method. In this work, various parameters like pushover curve, displacement vs base force, story displacement, hinges formation are obtained for all the models.Outrigger at optimum level at 0.5 Height gives better results in both displacements and base force. To sustain peak lateral loads these systems are provided half of the height. These study gives has inelastic behaviour of structure.

Applications of hysteretic steel dampers for controlling the seismic damage in steel frames

The aim of seismic design is not intended to make earthquake-proof structures that will not experience any damage even during a strong earthquake; such structures will be too costly. However, controlling the damage to the desired level is a necessity for buildings with a particular purpose such as hospital, fire and police station, nuclear facilities, buildings that contain hazardous material, and other building that is critical for emergencies and defense. In this paper, a four-story steel frame, both with and without hysteretic steel damper are investigated in order to account the effect of stiffness ratio, and SR (ratio between steel damper and braces stiffness to the bare frame stiffness) in the global structural damage. For these purposes, three ground motions which are compatible to the design spectrum response in the Indonesian building code were selected to be applied to the structure with a stiffness ratio (SR) of 2, 3, 4 and 5 using a non-linear dynamic time history analysis. In this context, the damage index based on the works of Park and Ang is used as the criteria to define global structural damage, while story drift index is used as the criteria to measure the seismic performance level. The results demonstrated that the use of steel damper not only enhances the seismic performance, but it also reduces the damage index of the investigated structure. Furthermore, the damage index and story drift index are influenced by the stiffness ratio, in which the stiffness ratio of 4 (four) provides the smallest damage index and inter-story drift index. Moreover, the damage index and inter-story drift index were also affected by ground motions characteristics.

An experimental study on the effect of frame-to-wall connection type on the seismic behavior of steel frames infilled with autoclave-cured aerated concrete blocks

In this article, in order to find some reliable connection types for avoiding the infill failure, an experimental study is conducted on six half-scale single-story single-bay specimens, including one bare frame and five steel frames with autoclave-cured aerated concrete walls, each having different frame-to-wall connection types. Polyurethane adhesive was used in bed joints of the autoclave-cured aerated concrete walls as a mortar. The specimens were tested under displacement-controlled loading to examine their effect on the in-plane behavior of steel frames. The results suggested that V- and T-shaped connectors can be used as prequalified connectors between the wall and the frame. In specimens with these connectors, the interaction between infill and frame was ignorable and the infill remained intact up to life safety performance level (2.5% drift ratio). Furthermore, the application of these connectors resulted in a two-level performance of the infill whereby the frame stiffness degradation and strength deterioration after the drift ratio of 2.5% was compensated.

Evaluation of Steel Stairwell Dynamic Characteristics, Under Few Mass Configurations Using Ambient Vibration Method

Application of external mass on existing emergency steel stairwell in this study has altered the natural frequency when the resonance threshold has been reached and allows disruption to the human comfort feeling. Ambient vibration testing and modal analysis were carried out on 6 meter height of emergency steel stairway portal frame by using 1 Hz of tri-axial seismometer sensor and open source software of GEOPSY as the processing tool. The stairwell platforms were subjected by cumulative ascending static mass configurations of 300 kg, 600 kg and 900 kg. Identification of the predominant first mode frequency, f1, and mode shapes were made with specified empirical filtering protocols were applied. Fourier Amplitude Spectra (FAS) was used to transform the ambient vibration time series, when the first predominant frequency under bare frame (BF) condition shows at 8.32 Hz. f1 decreased linearly to 7.35 Hz (BF+300kg), 6.77 Hz (BF+600kg) and 6.23 Hz (BF+900 kg), when the masses were increased. In addition, at these frequencies’ ranges, bad human subjective experiences could be triggered as recommended by previous researchers between 8 to 5 Hz. Besides, the deflection shapes from the first mode frequency was also illustrated at higher deflection amplitude to one of the portal frame’s column which resisting two stairwell platforms. These amplitudes are higher when f1 is decreasing. It can be concluded that, ambient vibration approach has efficiently evaluated the dynamic characteristics and its influence against the structure-person interaction on existing steel stairwell portal frame in this study. Further strengthening work on the steel frame could decrease the reductions percentages of the predominant frequencies, deflection amplitudes and even increase the human comfort level when using the stairwell, especially during building evacuation procedure.

Comparing seismic performances of pilotis and bare RC frame structures by shaking table tests

This study investigates the role of masonry infill walls in the responses and failure modes of RC frames subjected to earthquake, by applying shaking table tests on two three-story, two-bay, 1/4-scale RC frame structures. Two types of RC frame structures, an infilled RC frame without infill walls in the first story (pilotis frame) and a bare RC frame, are constructed according to the seismic design codes of China. The pilotis and bare frames are simultaneously deployed on a shaking table when I-ELC180 ground motion and Wolong ground motion excitations are used. The two specimens are subjected to a sequence of dynamic tests with increasing intensity. This paper mainly presents and compares the phenomena observed from the shaking table tests of the pilotis and bare frames, including the dynamic properties, acceleration and displacement responses, evolution of damage and final failure mechanisms. The tests indicate that, compared with the bare frame, the infill walls in the pilotis frame can significantly affect the failure mode and damage distribution. Plastic hinges first appear in the 1st story columns for the pilotis frame under seismic loading, while plastic hinges first appear at the beam ends in the 1st story for the bare frame; The damage to the pilotis frame is increasingly concentrated in the 1st story as the earthquake intensity increases, while the damage distribution along the height of the bare frame remains almost the same as the earthquake intensity increases. The maximum interstory drift ratio of the pilotis frame is up to 50% larger than that of the bare frame under the same earthquake intensity.

Modeling criteria of older non-ductile concrete frame–wall buildings

The purpose of seismic provisions included in modern building codes is to obtain a satisfactory structural performance of buildings during earthquakes. However, in the United States and elsewhere, there are large inventories of buildings designed and constructed several decades ago, under outdated building codes. Some of these buildings are classified as non-ductile buildings. Currently, under the ATC-78 project, a methodology is being developed to identify seismically hazardous frame–wall buildings through a simple procedure that does not require full nonlinear analyses by the responsible engineer. This methodology requires the determination of the controlling plastic collapse mechanism, the base shear strength, and the ratio between the story drift ratio and the roof drift ratio, called parameter \(\alpha\), at collapse level. The procedure is calibrated with fully inelastic nonlinear analyses of archetype buildings. In this paper we first introduce an efficient scheme for modeling frame–wall buildings using the software OpenSees. Later, the plastic collapse mechanism, the base shear strength, and values of \(\alpha\) are estimated from nonlinear static and dynamic analyses considering a large suite of ground-motion records that represent increasing hazard levels. The analytical experiment included several frame–wall combinations in 4 and 8-story buildings, intended to represent a broad range of conditions that can be found in actual buildings, where the simplified methodology to evaluate the risk of collapse can be applicable. Analysis results indicate that even walls of modest length may positively modify the collapse mechanism of nonductile bare frames preventing soft story failures.

Effect of infill walls on mechanisms of steel frames against progressive collapse

In this study, the effect of masonry infill walls on the progressive collapse mechanisms of steel frames is investigated. Three two-story by four-bay steel frames are designed: a bare frame, frame with full-height infill walls, and frame with partial infill walls. The applied vertical load, horizontal displacement, failure modes, stress development, and load redistribution mechanisms are investigated under center column pushdown scenarios. The influences of critical material properties and opening dimensions of partial infill walls are also investigated in this study. The results indicate that masonry infill walls significantly enhance the maximum applied vertical load and initial stiffness; however, they decrease the ductility and can alter the failure modes of the steel frames. The outward movement of the steel frames is a result of the diagonal compressive actions of the infill walls, and the changes in the bending positions of beams are a result of the bracing effects of the infill walls. The mortar joints and opening dimensions significantly influence the progressive collapse performance of infilled steel frames. In addition, different modeling strategies for masonry infill walls are developed and compared. Finally, a preliminary design procedure adopting masonry infill walls to protect the steel frames against progressive collapse is proposed.

Numerical Modeling of Masonry Infilled Reinforced Concrete Building during Construction Stages Using ABAQUS Software

The effects of seismic actions on reinforced concrete (RC) structures are strongly influenced by the dynamic behavior of their materials. It is crucial to find a simple definition of the natural frequencies of reinforced concrete buildings, particularly in relation to both principal and secondary elements constructing the reinforced concrete building type. This paper firstly presents a comparison with the ambient vibration surveys. An analysis model of different stages of construction of the reinforced concrete masonry wall was compared using the finite element software. In the second step, structural responses of the model were investigated by means of static analysis. Three main types were examined: Bare frame for one, two and three storeys; brick-walled; and coated cases. Modal analysis is carried out by ABAQUS software starting from the deformed building, to provide the natural frequencies and mode shapes. For the natural frequencies, a good agreement is obtained between analytical and experimental results. Furthermore, the comparison results between different cases show that the application of the plaster work increases the lateral stiffness and has significant effects on the dynamic response of the buildings.