Short Column Effect Research Articles

Solving the Problem of Short Column Effects in Masonry Infilled RC Frames: Numerical Investigations

In this study, the common issue related to the masonry infilled reinforced concrete (RC) frames under earthquake loading has been investigated. Namely, infilled RC frames are used in construction sector all over the world since they are easy and fast to construct. However, every medium to strong earthquake showed that this system is highly vulnerable to the seismic effects. Significant damage of infill walls, but also of the load carrying frame system demonstrates that stiff mortar connection between brittle masonry and highly deformable RC frames is not adequate. Damage of infilled RC frames lead to the high amounts of losses after earthquakes. Therefore, there is need to improve this behavior. Several problems caused by the infill/frame interaction have been investigated for decades and different approaches for modelling and improvement have been proposed. However, still there is no consensus on the modelling approach for infilled frames, as well none of the proposed solutions has not been accepted in practice. The most promising solution is to decouple infills from the frames and in this way diminishes negative effects of infill/frame interaction. This paper focuses on the short column effects, where infill walls increase shear forces in the columns, thus causing their damage. The numerical investigation of the short column effects on the traditional and decoupled infill has been presented. The analysis shows that the proposed decoupling system significantly improves the behavior of infilled RC frames. Infills are not activated by the frame deflection under earthquake loading and infills are not causing increase of forces in the surrounding frame. Results confirm that decoupled infills behave much better than traditional infills where contact between frame and infill has been achieved via mortar. Much higher in-plane drifts can be reached by using the decoupling INODIS system.

Drift-based fragility assessment of nonductile reinforced concrete columns failing in shear under cyclic loading

The paper presents drift-based fragility functions for nonductile reinforced concrete (RC) columns having light transverse reinforcement steel ratio which predominantly fail in shear. These fragilities were developed for four key damage states (i.e., light cracking, severe cracking, shear failure, and loss of axial load carrying capacity) associated with their structural performance observed in laboratory tests and repairability. For this purpose, experimental results of 71 column specimens tested under cyclic lateral loading were collected from 22 research programs; particularly, drift ratios associated to the column specimens tested to reach axial collapse. It is shown that the shear span-to-depth ratio and level of axial load ratio have influence on the drift-based fragilities associated to the damage states considered in this investigation. Additionally, several sources of epistemic uncertainty due to specimen-to-specimen, finite-sample, column shear span-to-depth aspect ratio, and level of axial compression load were quantified from the experimental database. The introduced drift-based fragilities are a very useful tool to assess the expected damage of existing buildings, such as school buildings that might exhibit the short captive column effect.

Study on the RC Frame with the Partial Infill Wall in Pushover Analysis

The short column effect is a major contributor to structural failure during seismic events. However, while most investigations concentrate on its influence on external walls, it also causes damage to interior walls. This underscores the significance of exploring interior wall damage due to this effect. This study involves four variations of RC frames with infill walls, analyzed using the Pushover method within the SAP 2000 software. The Pushover analysis vividly portrays the behavior and performance of interior wall systems. A comprehensive comparison of metrics like base shear, column shear force, and plastic hinge behavior underscores the pivotal role of interior walls in the entire structure, accentuating the necessity of delving into interior wall research.

Fragility curves for assessment of seismic vulnerability of buildings on slopes

Step-back and step-back setback configurations are the common structural systems found in the hilly regions of the Indian Subcontinent. These buildings are often subjected to torsional effects under the action of earthquakes due to different foundation levels. The present study focuses on the probabilistic determination of the seismic vulnerability of step-back and step-back setback configurations and the effects of live load eccentricity. Incremental Dynamic Analysis (IDA) is used to obtain the dynamic capacity curves, which capture the torsional effects. A set of 11 ground motion time histories have been selected and scaled to the target response spectrum. Fragility analysis is carried out after obtaining the dynamic capacity curves, and the fragility curves are obtained for five limit states, namely Operational Performance (OP), Immediate Occupancy (IO), Damage control (DC), Life Safety (LS), and Collapse Prevention (CP) as per FEMA 273. Comparison of the fragility curves indicates the suitability of the step-back setback configuration vis a vis step-back configuration, as it yields a low probability of damage. The short column effects, along with live load eccentricity, increase the vulnerability to damage.

Rapid seismic visual screen method for masonry infilled reinforced concrete framed buildings: Application to typical Sri Lankan school buildings

Seismic rapid visual screening (RVS) methods are used when a large stock of structures is to be evaluated for seismic risk. Although several RVS methods are available, applications of those methods to appraise the seismic risk of reinforced concrete framed (RC) buildings with irregularities in masonry infill walls (MIWs) are limited. School buildings constructed in Sri Lanka are built with certain RC frame typologies; however, they vary in terms of MIW arrangements used. Therefore, a new RVS method is proposed to evaluate the seismic risk of masonry infilled reinforced concrete (RC-MIW) buildings, particularly for the typical RC-MIW school buildings in Sri Lanka. The proposed RVS method incorporates irregularities of MIW arrangements in the typical RC buildings, the attributes of which are not well accounted in the available RVS methods. The vulnerability attributes such as short column and soft storey effects, arise due to the irregularities of MIW arrangements in the buildings, are explicitly incorporated in the proposed RVS method. The FEMA P-154 guidelines were followed to develop basic scores, score modifiers and minimum scores in the proposed RVS method. For that purpose, seismic performances of RC-MIW schools with various MIW irregularities were numerically analysed. The effectiveness of the proposed RVS method is compared with the existing RVS methods to evaluate the seismic risk of typical RC-MIW school buildings in Sri Lanka. It is shown that the proposed RVS method is capable of capturing the seismic risks of such typical RC-MIW Sri Lankan school buildings.

Influence of Infill on Reinforced Concrete Frame Resting on Slopes under Lateral Loading

When compared to traditional reinforced concrete constructions on level surfaces, buildings situated on hills with slopes require additional consideration, particularly when seismic loading is an important factor. In hilly slopes, the ground-level columns of structures have different heights due to the nature of the slope, which leads to a short column effect. This paper represents an experimental and analytical investigation of the behaviour of reinforced concrete frames and their response in sloped regions of hills, in which global retrofitting techniques were adopted by providing solid infill in the short column effect zone for the columns in the same storey of differentheights. Numerical analysis was conducted on how infill affected the short column effect under lateral cyclic loads. It was discovered that compared to bare reinforced concrete frames, masonry infill greatly increased the lateral load-carrying capacity by up to 50%. In the meantime, the frame’s ability to dissipate energy increased linearly. After infill was added to the frame with the short column effect, the reinforced concrete structure’s different reactions, including ultimate load displacement, crack pattern, energy dissipation, and energy absorption, were examined. With the addition of a solid infill, the reinforced concrete structure’s lateral strength and energy dissipation capacity were increased by 2.45 times. The damage development on the reinforced concrete frame with infill and the short column effect was less impacted by lateral stress than the reinforced concrete frame without infill.

Modification methods for infilled RC frames with and without openings with slides and formed steel: Experimental study

In this article, four pseudo-static tests of infilled RC frames were performed, including an unmodified solid infilled RC frame, an unmodified infilled RC frame with opening and two innovative structural designed specimens for the two original ones respectively. The solid bricks were made of rice husk and Magnesium oxysulfate cement, which is a recently developed environmental friendly thermal insulating material in China. The results of the tests showed that the two modified infilled RC frames provided better seismic performance than two original specimens in ductility, out-of-plane stability, stiffness degradation, etc. The modification also diminished the short-column effect of the infilled frames with opening.

Experimental Study on the Effect of Fibers on Engineered Cementitious Composite Short Square Columns

Recent earthquakes severely damaged short columns due to high lateral stiffness and low ductility. Some conditions, such as reductions in the heights of some columns compared to others on the same floor, deep beams, partially buried basements, and non-structural walls, cause short column effects. The prominent characteristics of engineered cementitious composites (ECCs) reinforced with polyvinyl alcohol (PVA) fibers – including their high tensile strength, micro and multiple cracks, energy dissipation, high ductility, and strain hardening – lead to improved seismic performance and economic efficiency in structure elements. In this study, 11 ECC columns with different fiber fractions (0–1.5%) and aspect ratios (3–7), as well as one conventional concrete column, were tested and evaluated. The results showed that increasing fiber friction and shear aspect ratio increased the length of the plastic hinge zone and ductility by at least 50% and 100%, respectively. Furthermore, the failure mode changed from brittle shear to ductile shear.

WITHDRAWN: Experimental study on the behaviour of RCC in-filled frame resting on sloped ground level

Abstract The buildings located in hills with slope needs special attention in earthquake point of view while compare to that of the conventional RCC structures in flat surface. In hill slopes the ground level columns of structures will be of different height due to the nature of slope which leads to short column effect in shorter columns. This paper represents the Experimental investigation on the behaviour of RCC structures and its response in sloped regions of hills in which global retrofitting techniques was adopted by providing solid full infill in the short column effect zone where the columns in same storey of different heights. Through which the effect of infill on short column effect under lateral static cyclic loading was analysed. It was found that the Lateral load carrying capacity of RCC frame with infill improved significantly meanwhile the energy dissipation capacity of frame increased linearly. The various responses such as Stiffness, crack pattern, Energy dissipation and energy absorption of the RCC structure after the provision of infill in the frame with short column effect were experimentally analysed and studied. The energy dissipation capacity and lateral strength of RCC structure with short column effect were enhanced by provision of solid infill. In comparison with the RCC frame without infill, the damage evolution of frame with infill and short column effect was less affected under lateral load.

In-plane and out-of-plane seismic damage of masonry infills in existing r.c. structures: the case study of De Gasperi-Battaglia school in Norcia

A significant correlation between the in-plane (IP) and out-of-plane (OOP) damage propagation of masonry infills (MIs) is frequently observed after strong earthquakes, posing a serious problem as regards vulnerability of public buildings such as schools. The present work is aimed at identifying the effects of different IP and OOP modelling assumptions of MIs on their seismic damage. To this end, the state secondary school De Gasperi-Battaglia in Norcia (Italy), object of monitoring by the Department of Civil Protection since 2000, is investigated for the heterogeneity of infill typologies. The school is composed of a basement and three storeys above ground level, with a reinforced concrete (r.c.) framed structure having a long-shaped rectangular plan. Two typologies can be identified in terms of transverse layout of MIs: (i) double-leaf interior partitions, made of hollow clay bricks; (ii) double-leaf exterior infill walls, constituted by facade solid bricks paired with hollow clay bricks. In addition, partial height infills in the longitudinal direction, due to classroom windows, make the columns susceptible to short column effects. MIs are represented by a five-element macro-model predicting both in-plane (IP) and out-of-plane (OOP) behaviour through a horizontal nonlinear truss and four diagonal nonlinear beam elements, respectively. Stiffness and strength values in the OOP direction are also reduced considering the evolution of the IP damage. Three assumptions are investigated for the behaviour of structural MIs: i.e. elastic both IP and OOP; inelastic IP and elastic OOP; inelastic both IP and OOP. Bare and infilled test structures are subjected to biaxial spectrum-compatible accelerograms, to evaluate the IP and OOP damage levels and effectiveness of the OOP simplified verification proposed by seismic codes.

Shear behavior of captive- and short- column effects using different basalt aggregate contents

The captive-column and short-column effects are resulted from constructing nonstructural walls or facades to the structural system which restricts the ability of the column to deformlaterally, or from constructing horizontal structural elements at mid-height of the column leaving the column divided in two short segments, or can dynamically evolve during earthquakes when the nonstructural walls partially damaged leaving part of the column can laterally deform. This research is intended to investigate the shear capacity of these column effects as a result of using different replacement contents of basalt aggregates in medium strength concrete mix. The workability and the mechanical properties of concrete mixes using different basalt aggregates replacement content are measured and a general improvement is observed in the compressive strength and the tensile splitting strength as basalt replacement content increased to 75%. The shear strength of short columns tested under lateral load improves as the replaced aggregates increased. An equation is proposed to estimate the concrete shear strength at various basalt aggregate replacement contents.

Test on the anchoring components of steel shear keys in precast shear walls

Prefabricated reinforced-concrete shear walls are used extensively in building structures because they are convenient to construct and environmentally sustainable. To make large walls easier to transport, they are divided into smaller segments and then assembled at the construction site using a variety of connection methods. The present paper proposes a precast shear wall assembled using steel shear keys, wherein the shear keys are fixed on the embedded steel plates of adjacent wall segments by combined plug and fillet welding. The anchoring strength of shear keys is known to affect the mechanical properties of the wall segments. Loading tests were therefore performed to observe the behavior of precast shear wall specimens with different anchoring components for shear keys. The specimen with insufficient strength of anchoring components was found to have reduced stiffness and lateral resistance. Conversely, an extremely high anchoring strength led to a short-column effect at the base of the wall segments and low deformation ability. Finally, for practical engineering purposes, a design approach involving the safety coefficient of anchoring components for steel shear keys is suggested.

Seismic response of substandard RC frame buildings in consideration of staircases

During the seismic performance assessment of existing buildings, staircases are generally not taken into account as structural members but as dead load. Staircases, as secondary structural members, not only serve for connecting successive floors but also provide considerable amount of strength and stiffness to the building which can modify its seismic behaviour considerably. In this parametric study, the influence of staircases on the seismic response of substandard RC frame buildings which differ in number of storey and span, presence of staircase and its position has been examined. Modal Analyses and bidirectional Non-Linear Time History Analyses (NLTHA) were conducted to compare several engineering demand parameters (EDPs) such as inter-storey drift ratio (ISDR), floor accelerations, modal properties, member shear forces and plastic hinge distribution. Additionally, short column effect, variation in shear forces of columns that are attached to the staircase slab, failure and deformation in staircase models have also been investigated. As the staircase was considered in the analytical model, a different damage pattern can be developed especially in the structural components close to staircase.

Response Modification Factors of Non-seismic School Buildings Considering Short Column Effects and Natural Period

Response Modification Factors of Non-seismic School Buildings Considering Short Column Effects and Natural Period

Performance of reinforced concrete buildings and wooden structures during the 2015 Mw 6.0 Sabah earthquake in Malaysia

This paper discusses the outcome of an investigation which was conducted soon after the 2015 Sabah earthquake in Malaysia. Buildings in the affected area were mainly constructed from reinforced concrete (RC) and wooden materials. Although the Mw 6.0 earthquake imposed significant damage to the majority of RC buildings, no significant structural damage was observed for the wooden structures. It was found that damage to the RC buildings was mainly because of non-ductile detailing of the structural components, strong-beam weak-column condition, captive-column and short-column effects, soft and weak stories mechanism, irregularity in plan and elevation, unconfined gable/infill walls, bad workmanship, and the low quality of construction materials. It was observed that many wooden structures had flaws in their design and construction as well. However, because of the high strength-to-weight ratio and the flexible properties of wooden materials which allow them to undergo several cycles of deformation without breaking, they survived the seismic actions. This paper identifies and discusses the main reasons for the damage observed in RC buildings and the construction flaws that were observed for wooden structures. Recommendations from seismic design codes in order to prevent the occurrence of such damage in the future are also highlighted.

Response Modification Factors for Seismic Performance Evaluation of Non-seismic School Buildings with Partial Masonry Infills

Most school buildings consist of reinforced concrete (RC) moment frames with masonry infills. The longitudinal direction frames of those school buildings are relatively weak due to the short-column effects caused by the partial masonry infills and need to be evaluated carefully. In 'Manual for Seismic Performance Evaluation and Retrofit of School Facilities' published in 2018, response modification factor of 2.5 is applied to non-seismic RC moment frames with partial masonry infills, but sufficient verification of the factor has not been reported yet. Therefore, this study conducted seismic performance evaluation of planar RC moment frames with partial masonry infills in accordance with both linear analysis and nonlinear static analysis procedures presented in the manual. The evaluation results from the different procedures are compared in terms of assessed performance levels and number of members not meeting target performance objectives. Finally, appropriate response modification factors are proposed with respect to a shear-controlled column ratio.

Feasibility Studies on Adaptive Interface for Square Infilled Frame

Abstract High rise buildings are becoming more common nowadays to face the increasing demand on the land area for industrial and agricultural needs apart from urbanisation. Such buildings require special systems to carry lateral loads resulting from wind, earthquake etc. One of the more common lateral load resisting system is an infilled frame. Infilled frame is a structural system developed through the composite action between the bounding frame and the infilling wall under in plane lateral loads. Such an interaction has proved beyond doubt that an increase in the lateral stiffness of the bare frame. However there are certain limitations reported in the literature due to the composite action like increased base shear, short column effect, vertical stiffness irregularity, reduced ductility etc.It is worth considering development of a provision to make the frame to behave as an infilled frame during working load levels and converting its behaviour similar to that of ductile bare frame towards its failure stages. The main objective of the present investigations is to seek the evolution of feasibility of an infilled frame system whose stiffness can be altered during its service without altering physically any of the component materials. This is sought to be achieved in the present investigation by providing an air medium (pneumatic medium) at interface and altering the air pressure as required. Under main conclusions include the possible to alter lateral stiffness and cracking and failure load levels of infilled frame through use of pneumatic medium interface.

Feasibility Studies on Proactive Disaster Prevention in frames of sloped regions

Abstract Buildings located in sloped regions require extra attention compared to that of the buildings in flat ground as they have varying column heights leading to short column effect. This paper presents the analytical study of behaviour of RC frames in sloped regions in which three different techniques such as equating stiffness of the columns to that of the stiffness of short column thereby changing the cross section of the columns, providing infill, providing steel plates at regions of maximum shearare incorporated to alleviate short column effect under static cyclic loading, thereby proving to serve as proactive disaster prevention measures. The Maximum displacement and Ultimate load of the RC frame is determined. The Stiffness, Energy dissipation and absorption of the RC frame after implementation of the techniques are compared and analyzed.

A new method for infill equivalent strut width

Infills are as important members in structural design as beams, columns and braces. They have significant effect on structural behavior. Because of lots of variables in infills like material non-linear behavior, the interaction between frames and infill, etc., the infills performance during an earthquake is complicated, so have led designers do not consider the effect of infills in designing the structure. However, the experimental studies revealed that the infills have the remarkable effect on structure behavior. As if these effects ignored, it might occur soft-story phenomena, torsion or short-column effects on the structures. One simple and appropriate method for considering the infills effects in analyzing, is replacing the infills with diagonal compression strut with the same performance of real infill, instead of designing the whole infill. Because of too many uncertainties, codes and researchers gave many expressions that were not as the same as the others. The major intent of this paper is calculation the width of this diagonal strut, which has the most characteristics of infill. This paper by comprehensive on different parameters like the modulus of young or moment of inertia of columns presents a new formula for achieving the equivalent strut width. In fact, this new formula is extracted from about 60 FEM analyses models. It can be said that this formula is very efficient and accurate in estimating the equivalent strut width, considering the large number of effective parameters relative to similar relationships provided by other researchers. In most cases, the results are so close to the values obtained by the FEM. In this formula, the effect of out of plane buckling is neglected and this formula is used just in steel structures. Also, the thickness of infill panel, and the lateral force applied to frame are constant. In addition, this new formula is just for modeling the lateral stiffness. Obtaining the nearest response in analyzing is important to the designers, so this new formula can help them to reach more accurate response among a lot of experimental equations proposed by researchers.

Influence of Infill Wall Configuration on Failure Modes of RC Frames

An improper configuration of masonry infill walls in RC frame may lead to short column effect on the columns, which is harmful to the seismic behavior of the structure. In this study, a bare frame and two single‐story, single‐bay RC frames, partially infilled with masonry, were tested under cyclic loading. The failure mechanism and seismic performance of these partially infilled RC frames (with an infill height of 600 mm) with different types of connections were analysed. Based on the experiment, nonlinear finite element simulation and analysis were conducted to study the effects of the infill walls and connections. The results show that both mechanical performance and failure mode are affected by the infill height, the type of connection between the frame and the infill, and the ratio of shear bearing capacity of the frame column to that of the infill. For the masonry‐infilled frame with rigid connection, the higher the infill wall is, the lower the shear bearing capacity ratio will be. Thus, the effect of the lateral constraint of the infill wall on the column increases, and the shear span ratio of the free segment of the column decreases, resulting in the short column effect. Based on the analysis results, a value of 2.0 is suggested for the critical shear bearing capacity ratio of the frame column to the infill wall. If the shear bearing capacity ratio is less than 2.0 and the shear span ratio of the column free segment is not more than 2.0, the short column effect will occur. For the infilled frame with flexible connection, both the lateral constraint from the wall to the column and the wall‐frame interaction decrease; this reduces or prevents the short column effect. The conclusion can present guidance for the design and construction of masonry‐infilled RC frame structure.