Infilled Frames Research Articles

Seismic performance analysis of multi-span masonry infilled RC frame based on analytical strut model

According to previous studies, it was accepted that masonry infills have a contribution to lateral strength, stiffness, and ductility of reinforced concrete (RC) frames structures. In the past studies, an analytical method of diagonal strut model has developed for evaluating the seismic performance of masonry infill. In this model, the masonry infills were presented by compression struts as distributed forces at the frame-infill interfaces in which the frame-infill contact lengths were evaluated by static equilibrium related to compression balance and lateral displacement compatibility. The lateral strength of infill was determined based on frame-infill contact length. In the current study, an experimental study of quasi-static cyclic lateral loading tests was conducted to evaluate the seismic performance of two-bay brick masonry infilled RC frames. This paper discusses the results of seismic performance brick infills based on experimental and analysis results of the multi-span masonry RC frame applying the diagonal strut model. According to the analytical model, antisymmetric strut was acted at the top and bottom of the middle column of the multi-span infilled frame from each infill. As a result, good agreements of lateral strength of structures were obtained between the experimental and analytical values.

철골 가새 및 끼움골조로 보강한 기존 철근콘크리트골조의 내진성능평가

철골 가새 및 끼움골조로 보강한 기존 철근콘크리트골조의 내진성능평가

Multi-strut macro-model for masonry infilled frames with openings

This study aims to propose a multi-strut macro-model, capable of simulating the overall force-displacement behaviour of infilled frames with various opening configurations. For this purpose, the results of finite element modelling calibrated against several experimental data are employed to determine the characteristics of a multiple-strut model for such infilled frames. The results indicate that the size of the opening along with its position, compared to the size of the infill wall, can significantly affect both the inclination and also the effective width of the struts and therefore, the overall behaviour of infilled frames with opening. The proposed model is evaluated parametrically against FEM numerical results, with varying characteristics such as opening size and position, opening height-to-length ratio, height-to-length ratio of the infilled frame and relative rigidity of frame to the infill wall. The comparison of the derived results with the analytical and experimental findings demonstrates the ability of the model to approximate the lateral response of infilled frames with openings in a reliable and robust manner. A simple reduction factor for the ultimate strength of the perforated infilled frames is proposed based on opening size relative to infill wall size as well as relative stiffness of the frame and infill wall.

Stick-IT: A simplified model for rapid estimation of IDR and PFA for existing low-rise symmetric infilled RC building typologies

The prediction of seismic performances of buildings in terms of engineering demand parameters EDP, such as interstorey drift ratios IDR and peak floor accelerations PFA, represents a fundamental step towards the assessment of potential direct economic losses.This paper proposes a simplified model for the rapid assessment of EDPs in infilled moment resisting frames subjected to seismic loadings suitable for large scale assessment studies. The proposed model, named Stick-I (Stick model for Infilled frames), is a multi-degree of freedom MDOF system consisting of a series of lumped masses connected by means of nonlinear shear link elements. The shear link behavior is suitably calibrated adopting a multi-objective Genetic Algorithm procedure that employs the results of nonlinear cyclic pushover analyses performed on refined nonlinear FEM. Based on the regression study performed on a suitably generated Stick-I model database, a more general Stick-IT model, representative of RC Infilled frame Typologies of assigned storey number and dimensions in plan, is introduced. Simplified formulas for the definition of Stick-IT model are proposed depending on low-level information data that can be easily retrieved from rapid on-site surveys or remote sensing techniques.Both Stick-I and Stick-IT models are validated comparing the results of NRHA performed on refined FEMs with the results obtained adopting the simplified models and good agreement in terms of maximum EDP values and distribution along the building height is obtained.The typological Stick-IT model, which is defined as a function of few geometric and mechanical parameters, can be easily applied for simplified evaluation of expected response for building typologies. Hence, it can also be usefully employed for assessment of direct losses at the large scale, with a significant reduction in computational burden with respect to more refined methods.

Effects of infilled wall opening on load resisting capacity of RC frames to mitigate progressive collapse risk

To quantify the load redistribution capacity of infill walls in reinforced concrete (RC) frames to resist progressive collapse, a series of five 1/4 scaled RC frames with or without infill walls were tested. The two-bay and three-story RC frames were tested using a pushdown loading regime. It was found that the infill walls could increase the first peak load by 256%. Even with an opening ratio of 31%, the infill walls could still increase the first peak load by 88%. This could be explained as the first peak load of infilled frames was attributed into equivalent struts of infill walls while the first peak load of bare frame mainly attributed in the flexural action of the beams. Beyond expectation, infill walls may not reduce the deformation capacity of the frames and secondary short struts of the infill walls could enhance the load resistance of the frame in large deformation stage. The opening ratio of 11%, 16%, and 31% could decrease the first peak load of the infilled frames with solid walls by 13%, 25%, and 47%, respectively. Moreover, the infilled walls with or without openings may change the position of rebar fracture of the beams. Thus, it was incorrect to simplify multi-story infilled frames into single-story substructures.

A new procedure to determine equivalent strut of infill walls with openings for engineering applications

In architecture, design of doors and windows for functional requirements, circulation, natural light and ventilation, aesthetics and view is inevitable. Parameters such as size, location and aspect ratio of the openings change the seismic behaviour of infilled frames. Ignoring these parameters in structural analysis may lead to substantial inaccuracy in predicting the lateral stiffness, strength and ductility of the frame. Despite numerous experimental and numerical studies on perforated infill walls in recent decades, the related provisions are rare in seismic codes and engineers tend not to use their results in analysis and design due to their complexity. The main purpose of this work was to propose a new procedure to determine the specifications of equivalent struts of perforated infill walls for engineering applications considering structural stiffness and load path based on valuable existing literature. All common types of windows used in architectural design (central openings, eccentric openings, corner openings and full-length openings) were investigated and the literature was reviewed for reduction factors of equivalent struts of infill walls with openings. Where there was a lack of studies, 27 micro models and 14 macro models were analysed to achieve the purpose of the research. A comprehensive and practical algorithm based on the size and location of openings is proposed.

Effect of prior in-plane damage on the out-of-plane performance of concrete masonry infills

This paper presents results of a study on the out-of-plane behaviour and strength of concrete masonry infills bounded by reinforced concrete (RC) frames with prior in-plane damage. The experimental portion of the study consisted of testing of four physical infilled frame specimens at varying levels of in-plane damage. A finite element (FE) model was concurrently developed and validated using the test results. A parametric study using the model was performed to further study the effect of several influential geometric and material parameters including infill aspect ratio, masonry strength, and slenderness ratio. The correlation between the prior in-plane damage sustained by the infill and its out-of-plane strength as affected by each parameter was discussed in detail. The impact of cyclic vs. monotonic loading was also studied. The efficacy of the existing analytical method for calculating the strength reduction was evaluated using both the experimental and FE results. A new reduction factor equation was proposed and the comparison with the existing analytical method against the available results showed an improvement in providing an estimate of residual out-of-plane strength for infills with prior in-plane damage.

Architectural and engineering design criteria for earthquake resistant masonry infilled RC frames containing openings

In earthquake resistant design of RC frame structures, the definition of masonry infilled frame is often split between reinforced concrete and the masonry structures. However, it is known that the frame elements and the masonry wall work as a coupled system. Additionally, a dedicate chapter for the definitions of openings size, quantity and position is missing. The definition of a full, partial or non-masonry infilled frame with opening is not establish in engineering and architectural codes; rather, recommendations are given. A competent masonry infilled frame with openings would mean to correlate the architectural and engineering concepts as to define an engineered or non-engineered infilled wall. Likewise, certain boundaries should be established using both the architectural and engineering concepts to relate the importance of illumination and air ventilation product of the openings and masonry infilled frame failure patterns.

AN INVESTIGATION OF RETROFITTED MASONRY-INFILLED FRAMES (RMIF) WITH HYBRID FIBERS: AN EXPERIMENTAL APPROACH

A reinforced concrete frame with masonry wall infill, “framed-brick work”, is a composite basic structure demonstrated to be feasible and effective on account of in-plane smooth excitations. Numerous models have been proposed for simulation of the behavior of masonry infills. The act of utilizing infill walls has been under investigation as it has both positive and negative impacts on the behavior of the structure under horizontal load. An enormous number of experimental and diagnostic examinations have been embraced in the past to research the behavior of such frames. The paper has focused on the working principles and the fundamental highlights of a recently created retrofitted masonry infill frames (RMIF) with carbon fiber–reinforced polymer (CFRP) sheets of RMIF. The presence of CFRP retrofitted in infill frames changes the behavior of the structure under substantial loads. The behavior examination, for example, deflection, ductility and tensile strength, is investigated for clay brick and fly ash bricks examples. For approval reason, this investigation utilizes feed forward back propagation neural network (FFBN) procedure. The correlation between experimental and the predicted values demonstrated that while the mechanical properties can be predicted for each specimen up partly by a portion of these models with the exact outcome achieved as a minimum error.

Retrofitting of Infilled Frame in Reinforced Concrete Structure

This research work aims to compare the seismic performance (in terms of lateral load strength, stiffness, ductility, response modification factor and performance levels) of full scale infilled frames before and after retrofitting. To evaluate the seismic performance, two infilled frames with door opening at different locations were constructed in the laboratory based on the current construction practices in Pakistan. In one infilled frame, door opening was at the center (Frame-1) while in other, door opening was at a side (Frame-2). After construction, both the specimens were tested with quasi-static test. The damaged parent specimens were then retrofitted with Ferrocement overlay and cracks in the infill wall were repaired with grout injection. Steel door frames of gauge 18 were installed at the door opening to make the model more realistic. Results obtained after performing quasi static test on the retrofitted specimen have showed that the specimens not only gained the original strength, but the seismic parameters of the infilled frames were observed to have also improved.

Irregularity Effects of Masonry Infills on Nonlinear Seismic Behaviour of RC Buildings

Despite extensive research studies, the seismic response of infilled reinforced concrete buildings remains an open problem due to both the complexity of the interaction between the infill and the frame and the large number of parameters involved. Thus, guidelines for both modelling and analysis are still lacking and the infill walls are normally treated as nonstructural components in seismic codes. However, it may be not conservative to neglect the influence of infills. In fact, the infill masonry walls may significantly affect the stiffness, strength, and energy dissipation capacity of RC buildings, even when they are regularly distributed. Recognizing this influence and its importance on the vulnerability of infilled frames, Eurocode 8 requires amplifying seismic action effects due to infills. In this paper, the effectiveness of the Eurocode 8 design provisions for infill irregularity in plan and/or elevation was investigated. To this aim, different in-plan layouts of infill walls were selected as marginal cases for which Eurocode 8 does not require amplification of the action effects due to the presence of infills, or the additional measures to counteract these effects are not mandatory. The seismic vulnerability of the infilled RC buildings was evaluated using nonlinear static and nonlinear dynamic analyses. Both cracking and crushing of masonry and stiffness and strength degradation were considered in the analysis. The effect of the layout of the masonry infills on the seismic response in terms of resistance and displacement was evaluated. Results show that in one of the case studies here examined, it is not conservative to neglect the influence of infill panels. In fact, structural failure due to torsion and soft-storey effects may occur even in cases where Eurocode 8 does not require the amplification of the action effects. Finally, the total shear demand on columns may be underestimated, even in cases where the code provisions for infills irregularity are not mandatory, and the additional shear demand in the columns induced by the masonry infill is very low.

Simulations of corrugated steel bracing reinforing infilled RC frame: influence factors

Based on the experimental infilled reinforced concrete (RC) frames strengthening by corrugated steel bracing, finite element (FE) analysis is carried out to compare with experimental research. Hysteresis curves, envelope curves, stiffness curves and failure modes of the corrugated steel bracing are studied to reveal the structural performance. Corrugated steel bracing is designed to resist lateral load in reinforcing concrete buildings. The results show that the deviations of the yield loads between test results and simulation are 11.1 % (forward direction) and 9.17 % (backward direction); the maximum loads between test results and simulation are 9.09 % (forward direction) and 6.52 % (backward direction), respectively. Ten models are studied to considering the key factors of corrugated steel bracing. The results show that the stiffness and maximum loads (forward and backward) are improved as the thickness increases. The ductility is reduced as the thickness increases.

Review on Failure Modes of Masonry Infill Frames

Review on Failure Modes of Masonry Infill Frames

Out-of-plane Response of an Innovative Masonry Infill with Sliding Joints from Shaking Table Tests

ABSTRACT Within the European FP7 Project “INSYSME”, the research unit of the University of Pavia has developed a seismic-resistant masonry infill system with original details, which subdivides the masonry panel into horizontal stripes through the insertion of “sliding joints” and deformable joints at the infill–frame interface. The out-of-plane stability is governed by the flexural/arching resistance of the masonry stripes and adequate supports at the RC columns. An extensive experimental campaign has been performed. In this paper, the results of the out-of-plane dynamic tests on shaking-table conducted on the specimens with and without opening are discussed. These types of tests, never applied before on innovative masonry infill typologies, have involved a very demanding testing protocol, constituted of artificial input motions at increasing intensity. To interpret the test results and provide first indications for safety checks, simplified numerical and analytical simulations of the tests have been conducted. According to the out-of-plane experimental performance of this innovative infill system and to the satisfactory in-plane response, the solution appears to be very promising for real applications.

Experimental behaviour on seven storeyed infilled frame with pneumatic interface pressure

Abstract High rise buildings have now become order of the day in developed and developing countries. Population explosion, fast urbanization etc., and to take over the available land space, to meet this challenge high rise buildings are constructed more. But high rise buildings have to be designed not only for heavy vertical loads but also for considerable lateral forces. In this study the analytical investigation on seven storeyed prototype frames has suggested that the lowering the lateral stiffness of the entire infilled frame is possible by just altering the interface pressure in all seven storeys (10psi to 30psi). Further the cement mortar interface at first storey alone needs to be replaced with pneumatic interface in order to minimize lateral stiffness of entire frame. The experimental investigations, on the seven storeyed frame models have shown that the increase in interface pressure increases the lateral stiffness of the infilled frame. The cracking pattern of the infilled frame with interface pressure resembles that of a bare frame like mainly having cracks in the frame members. The masonry was found to be least affected. This indicates that the infill participation is very much reduced.

Analytical study on reinforced concrete two dimensional frame with knee bracing under cyclic loading

Abstract Structural bracing is normally used in steel structures to resist moments. In RC structures bracing is used as a retrofit technique to enhance the seismic performance of the building. But the scope of bracing as a concrete member is not as explored as concrete fails under tension. In my research project, I proposed a knee braced RC frame, where the bracing is provided as an RC member. Knee bracings are not so efficient compared to diagonal bracing, but it does resist moments and sway as well as allows passage through the frame. The objective of the project is to do an analytical model of a 2D RC frame; a bare frame; an infill frame; a knee braced frame. The lateral loading performance is compared within the three frames using cyclic loading. Displacement vs. time graph, load vs displacement graph is plotted for each frame to understand the performance of each frame under cyclic loading. The analytical work is done using finite element software.

Seismic performance of structures composed of T-shaped and L-shaped recycled concrete columns and lightweight infill walls

ABSTRACT In this paper, a structure composed of a T- or L-shaped recycled concrete column frame (RCCF) and lightweight infill wall (LIW) with a herringbone brace has been proposed to investigate its seismic behavior. Two T-shaped and two L-shaped full-size experimental models of the structure have been built and tested under low-cyclic loading conditions. Consequently, bearing capacity, stiffness, ductility, hysteretic behavior, energy dissipation, and failure characteristics of each test specimen have been analyzed, identifying structure parts prone to damage and failure, understanding their yield mechanisms, and lastly providing constructive recommendations for the structural design. Studies show that the bearing capacity, ductility, and comprehensive seismic behavior of T- or L-shaped lattice-reinforced RCCF-LIW structures with a herringbone brace have been significantly improved. For the engineering practice, it is necessary to strengthen the performance of the herringbone brace-frame beam joint.

Experimental study on a steel frame infill wall based on vertical partitioning technology

In this paper, a kind of steel frame infill wall is proposed wherein the primary and auxiliary partitioning schemes are vertical and horizontal partitioning, respectively. For this study, three full-size specimens were designed and built: a full-size specimen with a gate (Specimen G), a full-size specimen with two windows (Specimen W) and a full-size specimen with an empty frame (Specimen E). These specimens were subjected to in-plane and out-of-plane experiments in turn. The results showed that the wall constructed with the proposed technology exhibits a good in-plane seismic performance, low damage characteristics and a stable out-of-plane resistance. Although the design code states that a column should be set in the middle of the wall, the results of the out-of-plane test show that the out-of-plane resistance of the wall is stable without a column. This wall has a unique out-of-plane force transfer mechanism that provides this strong resistance. Moreover, the role of the vertical plank in this wall is similar to that of a column, so columns do not need to be added in the middle of the wall when using this new construction technology. Furthermore, this new construction technology can provide an important reference for the assembly and application of this type of wall in the future.

Influence of infill walls on modal expansion of distribution of effective earthquake forces in RC frame structures

It is quite apparent that engineering concerns related to the influence of masonry infills on seismic behavior of reinforced concrete (RC) structures is likely to remain relevant in the long term, as infill walls maintain their functionalities in construction practice. Within this framework, the present paper mainly deals with the issue in terms of modal expansion of effective earthquake forces and the resultant modal responses. An adequate determination of spatial distribution of effective earthquake forces over the height of the building is highly essential for both seismic analysis and design. The possible influence of infill walls is investigated by means of modal analyses of two-, three-, and four-bay RC frames with a number of stories ranging from 3 to 8. Both uniformly and non-uniformly infilled frames are considered in numerical analyses, where infill walls are simulated by adopting the model of equivalent compression strut. Consequently, spatial distribution of effective earthquake forces, modal static base shear force response of frames, modal responses of story shears from external excitation vector and lateral floor displacements are obtained. It is found that, infill walls and their arrangement over the height of the frame structure affect the spatial distribution of modal inertia forces, as well as the considered response quantities. Moreover, the amount of influence varies in stories, but is not very dependent to bay number of frames.

Influence of pneumatic interface pressure in reinforced concrete infilled frames

High rise buildings have now become order of the day in developed and developing countries. Allround population explosion, fast urbanization and rapid industrialization all try to take over the available land space, making it difficult to provide people their two basic needs viz food and shelter. Thus there is a pressing need to conserve and use judiciously the available land space. To meet this challenge are constructed, more and more of high-rise buildings which require relatively less ground space. In this study on prototype seven storeyed frame with an aim of studying the interactive effect of multiple floors being subjected to pneumatic pressure so as to find the possibility of controlling the entire infilled frame action through the control of any one floor and the practical aspects of replacing cement mortar interface with the proposed pneumatic interface. And also the Experimental investigation on one fourth scale model of seven storeyed single bay frames including developing of the test rig for lateral loading of the test specimen. The aim of this stage of studies is to practically verify the effect of introducing interface pressure on multi storeyed infilled frame.