Concrete Frame Buildings Research Articles

Performance Evaluation of Durability and Flexural behaviour of Self Compacting Concrete blended with Alccofine

Due to its superior performance over traditional concrete mixes, Self Compacting concrete (SCC) has increased in popularity in the construction industry in recent years. The major downside of using self-compacting concrete is that there is no universal design mix norm. The aim of this research is to determine the best mix proportioning and strength and durability parameters for M40 Alccofine based high strength self-compacted concrete. It often provides an exclusive application for self-compacting concrete since it can flow into any section of a heavily reinforced region without creating any vibration. Consequently, if using self-compacting concrete in beam-column joints does not adversely affect the frame’s seismic efficiency, it could be used rather than traditional concrete. During earthquake excitation, the beam-column joints of reinforced concrete building frames play a very important role. As those are the highly congested areas of reinforced concrete framed buildings, effective concrete placement and compaction in these regions is extremely difficult. This study involves determining the impact of Alccofine with replacement levels from 10 to 50 percentages with cement is substituted for M40 grades with Viscosity Modifying Agent, with both the purpose of increasing compressive strength, lowering gas emissions, and making concrete more cost efficient. In specific, increasing the CaO volume of the Alccofine 1203 increases the binding capacity and compressive strength.

Practitioner-friendly design method to improve the seismic performance of RC frame buildings

Reinforced concrete (RC) frame buildings are a widely used structural system around the world. These buildings are customarily designed through standard code-based procedures, which are well-suited to the workflow of design offices. However, these procedures typically do not aim for or achieve seismic performance higher than code minimum objectives. This article proposes a practical design method that improves the seismic performance of bare RC frame buildings, using only information available from elastic structural analysis conducted in standard code-based design. Four buildings were designed using the proposed method and the prescriptive approach of design codes, and their seismic performance is evaluated using three-dimensional nonlinear (fiber) models. The findings show that the seismic performance is improved with the proposed method, with reductions in the collapse fragility, higher deformation capacity, and greater overstrength. Furthermore, an economic analysis for a six-story building shows that these improvements come with only a 2% increase in the material bill, suggesting that the proposed method is compatible with current project budgets as well as design workflow. The authors also provide mathematical justification of the method.

Solar Bridge Retrofit System: An innovative solution to renovate structural thermal bridge areas

The structural components of load-bearing concrete frame buildings, such as concrete beams and columns, are critical elements of the facades which often act as a thermal bridge. To reduce the impact of structural thermal bridge areas in non-retrofitted Portuguese residential buildings, a new innovative solar passive retrofit solution, named Solar Bridge Retrofit System (SBRS), is proposed. This concept relies on the principles of unvented Trombe wall systems and consists in using an external transparent skin in front of the structural areas of the envelope in combination with the traditional ETICS in the remaining area. Contrary to the traditional Trombe walls, this innovative design enables the heavy structure of the building to absorb solar radiation and conduct the heat slowly inward or to the adjacent structure.To evaluate the thermal performance of the SBRS, an experimental setup was developed. The field results obtained during February and March 2020 for two different configurations, showed that the double-glazing configuration in combination with ETICS has the potential to improve thermal comfort and reduce energy consumption. This paper addresses both the design of the SBRS and the obtained results from the experimental work.

Natural period and vertical distribution of base shear in confined masonry buildings using ambient vibration test

In semi-urban setting where availability of land can afford construction of low-rise buildings, confined masonry may compete with other alternatives of seismic resilient system provided well-articulated design standards and construction guidelines are available. Most seismic standards do not make explicit recommendations on the natural period and vertical distribution of base shear for the design of confined masonry buildings. In such a case, one of the two alternatives, such as (1) reinforced concrete (RC) frame building with masonry infill walls and (2) RC frame building with structural walls, is tacitly extrapolated. This paper is first aimed to explore the possible recommendations from the ambient vibration testing of a class of confined masonry building stock. Nine (G + 3) confined masonry hostel buildings are considered for Ambient Vibration Testing (AVT). Recorded signatures are processed and modal characteristics (primarily restricted to the first triplet of fundamental modes) are extracted. Each building is modelled numerically and fine-tuned followed by a comparison of natural frequencies and mode shapes in numerical model and experimental results. The fine-tuned numerical models are analysed against a set of recorded ground motions. Possible design recommendations for natural period and distribution of base shear along the height are the key contributions. Empirical equation for natural periods is derived from the seismic code recommendation on that of reinforced concrete (RC) buildings but removing the bias contributed from the height shorter than one storey while using the experimental results. Distribution of the base shear along the height follows a parabolic profile with an exponent close to 0.4. Results of AVT indicate the inherent damping ratio on an average of about 5% which, however, may not be directly used for seismic excitation. The building stock used for AVT in this paper does not include considerable variations in height and different varieties of confined masonry constructions. Therefore, recommendations of this paper should be verified against a larger size of dispersed building stock.

System identification for a six-storey precast concrete frame building

This paper presents forced and ambient vibration tests on a six-storey precast concrete frame building, a structural system that has not often been the focus of such tests in spite of its widespread use. Precast buildings come with semi-rigid connections so their idealisation requires good knowledge of the construction practice for those connections and their details. Structural system dynamic properties are identified for the first three translational modes along each axis of the building and for the first three torsional modes. The study shows that the three-dimensional finite-element structural model for the building is capable of replicating the measured in situ dynamic properties. In the small displacement elastic range, the finite-element modelling of precast concrete frame systems is not very different from their cast-in-place counterparts but an extrapolation to the large displacement range requires empirical confirmation.

Effects of reinforcement corrosion on reinforced concrete buildings

The aim of this paper is to present the different effects of reinforcement corrosion on reinforced concrete buildings. A hypothetical five-storey reinforced concrete building frame was designed for this purpose. Three different modes of action were selected – corrosion on the ground floor alone, corrosion on one facade and corrosion on two neighbouring facades of the building. For each mode of action, different corrosion scenarios were selected, which were arranged in terms of mass loss from zero to 15% in ascending order an in 3% steps. Pushover analyses of the building were performed for each corrosion scenario and the results of these analyses were used to perform a structural performance evaluation conforming to Eurocode 8. A general decrease in structural performance was determined with significant changes in the dynamic characteristics of the building. The level of decrease depended on the corrosion scenarios and the modes of action. Important structural behaviour alterations and premature damage occurrences were found, in addition to a reduction in the displacement ductility of the building. For severe-corrosion scenarios, reductions in moment and curvature capacities could shift the structural behaviour of the load-bearing members from ductile to non-ductile.

Estimation of the effect of surface blast on buildings

A surface blast generates both air pressure and ground shock on structures. Studies on the relative effects of the air pressure and ground shock on the responses of structures are meagre. In the present study, a preliminary estimate of the relative contributions of the ground shock and air pressure on building responses due to a surface blast is obtained by using an equivalent single-degree-of-freedom (SDOF) model. For this purpose, both linear and non-linear analyses of SDOF models of four reinforced concrete building frames of different heights are performed under different blast scenarios by varying the standoff distance and charge weight. In addition, the criticality of the surface blast in comparison to the free air blast is investigated with the help of the same SDOF models. The study reveals that the contribution of the ground shock is less than that of the air pressure on the responses of low-rise buildings. For high-rise buildings, the opposite trend is observed for smaller standoff distances (R < 15 m). Further, it is shown that the surface blast is more critical as compared to the free air blast for shorter buildings (fewer than six storeys), but the opposite holds good for taller buildings.

Accounting for shallow foundation settlement in the analysis and design of multi-storey frame buildings: Development of a new software package

In this work we explain a new methodology that have been utilized in a new software package (program) to take into account the influence of foundation settlements in the analysis and design of 3D reinforced concrete frame buildings. We present the solution using a new load pattern in the program, named SETTLEMENT. Firstly, the program analyzes and calculates the displacements in the ground joints of the structure according to several methods of the prediction of the settlement of shallow foundations. Secondly, the program assigns these displacements in the ground joints and analyzes the structure under the influence of these displacements only, calculates the internal forces and the deformed shape of the structure, and stores these values within the results data of the SETTLEMENT load pattern. The program is based on finite elements method. It provides a drawing environment (3D view, plan view, elevation view) with tools to create the model and to perform the structural analysis and design.

Seismic analysis of reinforced concrete buildings with participating masonry infills

ABSTRACT In this paper, seismic analyses are performed of a reinforced concrete frame building with participating masonry walls are carried out. The spectral method of the Brazilian code – ABNT 15421:2006 – was used to obtain the lateral seismic loads. The equivalent diagonal-strut model was employed to simulate the axial stiffness of the masonry walls in the frames, according to different formulations founded in literature. The main purpose is to evaluate the differences implemented by the different formulations for the equivalent strut on the seismic response. This paper also aims at comparing results obtained when the masonry stiffness is not considered under seismic loads. The results obtained are analyzed with the purpose of providing contributions for structural engineers in the design of framed structure buildings with participating masonry walls subjected to seismic loads.

Reliability of a reinforced concrete frame building under earthquake

The research objective is performing probabilistic nonlinear dynamic seismic resistance analysis for the reinforced concrete building frame. The building design is compliant with SP 14.13330.2018 Construction Code. The LS-DYNA software was used for nonlinear dynamic analysis. A set of two-component accelerograms to be analyzed was generated. The set consists of 20 random seismic events with the specified expected values for the predominant frequency and the intensity. The structural response as random processes and values was studied. The resulting experimental response value distributions were fitted to distribution laws. The results showed that the K 1 factor accounting for acceptable damage to buildings and structures should be much larger than specified in the regulatory codes. It indicates that the seismic resistance of the building is insufficient in terms of the near-collapse failure criterion.

Evaluation of an accidental-torsion design proposal considering firm-soil ground motions

Using non-linear analyses and Monte Carlo simulations, a simplified accidental-torsion design procedure is evaluated. The design procedure does not use an accidental eccentricity like the building codes do. For the evaluation, four reinforced concrete frame building models of four and seven stories are dynamically studied in the nonlinear range. The models are subjected to a set of five firm-soil, bidirectional seismic records. The design procedure is evaluated by comparing the ductility demands of both beams and columns for three conditions of each building model: a) the torsionally balanced model without accidental torsion (model TB), which establishes the reference values of ductility demands; b) the same nominal model but incorporating accidental torsion via the Monte Carlo method; and c) a model with amplified strength (model AS) according to the accidental-torsion design procedure to be evaluated. Results indicate that there is a probability smaller than 2.5% that accidental torsion can cause ductility demands approximately 20% to 25% larger than those of similar building models without accidental torsion. A comparison of ductility demands for the reference models without accidental torsion and those of models with accidental torsion and designed with the procedure that is evaluated, reveals that the design procedure is effective to control the effects of accidental torsion.

ЖИВУЧЕСТЬ РАМНО-СТЕРЖНЕВОГО ЖЕЛЕЗОБЕТОННОГО КАРКАСА ЗДАНИЯ В ЗАПРЕДЕЛЬНЫХ СОСТОЯНИЯХ

A methodology and an algorithm for calculating the survivability parameters of a long-term deformable reinforced concrete building frame in extreme states are presented. Analytical dependencies for determining the value of the creep measure are taken in accordance with the use of approximate dependencies from the recommendations of the NIIZHB. On this basis, a method is proposed for determining the cross-section bending stiffness of the frame elements. The deformation criterion of a special limiting state is formulated taking into account the nonequilibrium processes of prolonged deformation of the structural system elements. The numerical analysis results of the long-term deformable reinforced concrete frame survivability potential with a sudden removal of the one structural element, taking into account the long-term deformation prehistory of the considered building frame under an operating load, are presented. The exposure of the structural system survivability from the its loading moment to its transformation into a kinematically variable system has been determined.

Foundation and Analysis of Multistoried High-Rise-Building

Analysis and design of buildings for static forces is a routine af- fair these days because of availability of affordable computers and specialized programs which can be used for the analysis. On the other hand, dynamic analysis is a time consuming process and requires additional input related to mass of the structure, and an understanding of structural dynamics for interpretation of analytical results. Reinforced concrete (RC) frame buildings are most common type of constructions in urban, which are sub- jected to several types of forces during their lifetime, such as static forces due to dead and live loads and dynamic forces due to the wind and earthquake. Here the present works (problem taken) are on a 35th storied regular building. These buildings have the plan area of 25m x 45m with a storey height 3.6m each and depth of foundation is 2.4 m. & total height of chosen build- ing including depth of foundation is 132 m. This paper describes seismic analysis of high-rise building using program in STA- ADPro. with various conditions of lateral stiffness system. The static and dynamic analysis has done on computer with the help of STAAD-Pro software using the parameters for the design as per the for the zones and the post processing result obtained has summarized.

Cost optimization of reinforced concrete frames using genetic algorithms

Cost optimization of reinforced concrete building frames using genetic algorithms is presented. Unlike previous works that used simplified discrete or continuous optimization models, this work considers constructability issues as well as the effects of shear and torsional actions in the design optimization of reinforced concrete frames. An integrated software system has been developed to implement the proposed optimization procedure using genetic algorithms. Examples have been incorporated in order to compare the results from the proposed study with that of a previous work which follows a different heuristic and with the traditional “design–check–revise” method. The structural design procedures recommended in the Eurocode-2 have been strictly followed in this work. Special emphasis has been given to structural analysis methods and studying computational efficiency of the developed framework. To improve the performance and computational complexity of the algorithm, the effect of genetic parameters such as mutation and crossover on the optimization process has been thoroughly studied. The method developed in this work proves to have a lot of advantages over the traditional “design–check–revise” paradigm and other heuristic methods.

Peak Velocity of Viscous Dampers for Direct Displacement Based Design of RC Moment Resisting Frames

ABSTRACT Previous researchers have extended the direct displacement-based design (DDBD) procedure, to design reinforced concrete moment-resisting frame (RC-MRF) buildings with linear viscous dampers (LVDs). In those studies, the viscous damper forces are found to be larger than the design viscous damper forces because the actual relative structural velocity is different from the pseudo-velocity and also due to higher-mode effects. In the present study, a damper velocity correction factor is introduced along the height of the RC-MRF with LVDs, to calculate the corrected velocity of the LVD from the design velocity of the LVD, when the DDBD procedure is used. The damper velocity correction factor is proposed using the results of nonlinear response history analysis (NLRHA) for a set of RC-MRFs with LVDs, which are designed using the DDBD procedure. The DDBD procedure is then used to design RC-MRFs with nonlinear viscous dampers (NLVDs) making use of the proposed damper velocity correction factor, by calculating the NLVD characteristics using the equal energy (EE) dissipation approach or the equal power (EP) consumption approach. The accuracy of the proposed damper velocity correction factor is evaluated by carrying out NLRHA of two sets of RC-MRFs with NLVDs, one set where the damper velocity correction factor is not used, and the other set where it is used. When the damper velocity correction factor is used; the design LVD forces either agree with NLRHA results or are slightly more conservative, the design NLVD forces are close to the NLRHA results, and the maximum value of peak inter-story drift ratio (IDR) along the height of the RC-MRF from NLRHA is close to the design IDR limit. There is no significant difference in the peak story shear forces whether the damper velocity correction factor is used or not.

System Identification and Seismic Performance Assessment of Representative RC Buildings in Kathmandu Valley

To identify dynamic characteristics of representative reinforced concrete frame buildings with brick infills, ambient vibration measurements were taken in two four-storied buildings—one situated in soft soil and the another in stiff soil. Non-parametric as well as parametric system identification (SID) algorithms were used to estimate vibration frequencies and damping of the two buildings. The numerical models of the buildings were created using the finite element method. The modal frequencies and damping ratios obtained from ambient measurements were used to calibrate and tune the finite element models. The comparison between measured vibration frequencies and those obtained from finite element model highlights the need for accuracy in modeling assumptions, in particular, consideration of the stiffness of infill walls and the flexibility of foundation soil. The finite element models calibrated with SID results were used to estimate the response of the two buildings when subjected to strong ground motion recorded at different places in the Kathmandu Valley during the 2015 Gorkha earthquake. The results show that not considering flexibility of foundation and stiffness of infill walls, as is commonly done in engineering practice, can lead to inaccurate estimates of seismic demand.

Progressive collapse capacity of a gravity-load designed RC building partially collapsed during structural retrofitting

The problem of progressive collapse has been a major topic in structural forensic engineering since its inception, but it has recently received a growing interest. In the last two decades, the occurrence of extreme events and their catastrophic impact on the built environment and people has promoted several research programmes and guidelines for structural design and assessment, spotlighting the importance of back-analysis and numerical prediction of progressive collapse phenomena. This paper presents a numerical study aimed at investigating the ability of existing reinforced concrete structures to prevent progressive collapse during structural retrofitting. The progressive collapse capacity of a real, reinforced concrete framed building constructed in the 1950s and partially collapsed in 2001 is discussed in relation to a couple of structural retrofitting operations that were found to be the primary causes of the accident. Existing information from past forensic investigations was integrated with a simulated design procedure to develop the capacity model of the structure, according to design codes and practice rules used at the time of construction. Nonlinear pushdown analysis with displacement control was carried out both in intact conditions and during retrofitting operations. In addition to global capacity models of the structure, the use of partial capacity models representing the building corner under retrofitting was evaluated, highlighting a very high computational efficiency of those simplified models. Analysis results also indicate that the load contribution from infill walls can significantly influence the progressive collapse resistance, particularly in relation to retrofitting works involving the corner of the building plan as actually happened. Retrofitting interventions on the real building included the concrete cover removal from ten ground-floor columns and soil excavation around column bases. The removal of concrete cover from single and multiple ground-floor columns together with the loss of supports due to soil excavation around column bases was found to significantly affect the collapse capacity of the structure. The major impact of retrofitting operations in terms of location and extent provides a simulation-based proof of the progressive collapse suffered by the case-study building, evidencing that soil excavation around more than three columns was able to produce the accident.

The Role of Infill Walls in the Dynamic Behavior and Seismic Upgrade of a Reinforced Concrete Framed Building

Masonry infill walls are commonly used in the frames of reinforced concrete (RC) buildings around the world. The seismic performance of these buildings is strongly affected by the presence of the infill walls and partitions, as shown by the post-earthquake damage in many cases. The effect of these components is particularly important for RC frame constructions underdesigned for seismic actions that usually are characterized by deformable frames magnifying the contribution of the infill walls to the seismic response. Also the flexibility of the floors could be influenced by the collaboration of the infill walls to the transversal stiffness of the building. The paper addresses the seismic assessment of a typical infilled RC frame building designed only for gravity loads in the 1960s in the Southern of Italy that currently is a high-seismic zone. The structural identification of the building based on ambient vibration test has been already done pointing out the significant role of infill walls and partitions through the updating of the numerical model. Based on the results of the calibrated model, the effect of the floor flexibility on the dynamic behavior of the structure is discussed, and the seismic capacity at life safety limit state (LSLS) is assessed by means of the linear dynamic analyses. The effects of the infill walls on the seismic performance of the building are discussed in detail considering a strengthening solution that involves the infill panels as masonry walls cut from the RC columns to avoid the local interaction but strengthened by composite grids in mortar matrix (FRCM).

Forced-based Shear-flexure-interaction Frame Element for Nonlinear Analysis of Non-ductile Reinforced Concrete Columns

An efficient frame model with inclusion of shear-flexure interaction is proposed here for nonlinear analyses of columns commonly present in reinforced concrete (RC) frame buildings constructed prior to the introduction of modern seismic codes in the Seventies. These columns are usually characterized as flexure-shear critical RC columns with light and non-seismically detailed transverse reinforcement. The proposed frame model is developed within the framework of force-based finite element formulation and follows the Timoshenko beam kinematics hypothesis. In this type of finite element formulation, the internal force fields are related to the element force degrees of freedom through equilibrated force shape functions and there is no need for displacement shape functions, thus eliminating the problem of displacement-field inconsistency and resulting in the locking-free Timoshenko frame element. The fiber-section model is employed to describe axial and flexural responses of the RC section. The modified Mergos-Kappos interaction procedure and the UCSD shear-strength model form the core of the shear-flexure interaction procedure adopted in the present work. Capability, accuracy, and efficiency of the proposed frame element are validated and assessed through correlation studies between experimental and numerical responses of two flexure-shear critical columns under cyclic loadings. Distinct response characteristics inherent to the flexure-shear critical column can be captured well by the proposed frame model. The computational efficiency of the force-based formulation is demonstrated by comparing local and global responses simulated by the proposed force-based frame model with those simulated by the displacement-based frame model.

Dynamic analysis of high-strength concrete frame buildings for progressive collapse

The issue of progressive collapse of two real-scale frame buildings examples (three and six stories) constructed from High-Strength Concrete (HSC with fc` =75 MPa) and Normal-Strength Concrete (NSC with fc` =32 MPa) under central column removal have been studied using numerical analysis. Initially, a finite element linear static analysis was carried out. Next, linear dynamic and non-linear dynamic analyses were conducted to account for the extreme dynamic effects that arise during central column removal. The values of Demand-Capacity Ratios are considered in each analysis. The results showed that, the analysis of progressive collapse under central column removal of three and six stories frame buildings constructed from HSC is approximately similar to that of the same structures constructed with NSC. The three stories building constructed from NSC and HSC would not be susceptible to collapse for linear statically central column removal, while the situation is reversed for both NSC and HSC six stories buildings. NSC and HSC three and six stories buildings would be susceptible to progressive collapse for linear and nonlinear dynamic central column removal. The ratio between the maximum nonlinear dynamic displacement and the maximum linear dynamic displacement for NSC and HSC three stories buildings at the column removal are 1.17 and 1.18, respectively, whereas these ratios become 1.89 and 1.86 for NSC and HSC six stories building, respectively. The internal forces at the most critical sections for NSC and HSC three story building in the case of linear dynamic analysis are larger than that of linear static analysis by about 58% and 39%, respectively, while for six story building these ratios become 82% and 80%, respectively. For the case of nonlinear dynamic analysis, these ratios for NSC and HSC three story building are larger than that of linear dynamic analysis by about 9% and 7%, respectively, while for six story building these ratios become 11 % and 8%, respectively due to activation of plastic hinges.