Strut Model Research Articles

Characterization of Equivalent Struts for Macromodeling of Infilled Masonry RC Frames Subjected to Lateral Load

AbstractEvaluation of the seismic performance of infill frame structural systems using equivalent strut models and pushover analysis has gained popularity due to the simplicity of the evaluation pr...

Estimating the local and global effects of infills on steel frames by an improved macro-model

Masonry infill panels change the seismic behavior and internal forces of surrounding frames and should be considered in analysis and design phases. Single equivalent strut model, the most common strut model, does not address the internal forces and therefore the multi-strut models are preferred. In this paper, the previously proposed three-strut model (model PD) has been improved to represent a more reliable prediction of both local and global infill effects. For this, an in-depth finite element sensitivity analysis is performed. It is shown that the new model estimates the bending moment and shear force distribution and predicts the stiffness and strength of the infilled steel frames more accurately than previously proposed models in the literature. Properties of the nonlinear hysteretic behavior of infilled frames including stiffness degradation and strength deterioration can also be determined precisely. Finally, the macro-model is further developed to capture the global seismic response and element force distribution of frames with a soft first story.

Computational modelling of strut defects in SLM manufactured lattice structures

Addition of manufacturing defects to computational models of 3D-printed lattice structures enable improved simulation accuracy. A computational model of a cellular structure based on finite element method (FEM) analysis, often starts from defect-free computer-aided design (CAD) geometries to generate discretised meshes. Such idealised CAD geometries neglect imperfections, which occur during the additive manufacturing process of lattice structures, resulting in model oversimplification. This research aims to incorporate manufacturing defects in the strut elements of a lattice structure, thereby enhancing predictive capabilities of models. In this work, a method of generating CAD AM representative strut models is proposed. The models are generated from micro-computer tomography (μCT) analysis of SLM fabricated struts. The proposed additive manufacturing (AM) representative strut FE model's axial stiffness and critical buckling load is compared to idealised- and μCT- based FE models, with significant error reduction over idealised strut models. The AM representative strut models are then used to generate full lattice FE models and compared with manufactured and idealised FE models. The AM representative FE lattice models show greater correlations toward experiment and more realistic deformation behaviours. Overall, the methodology used in this study demonstrates a novel approach to representing struts in FE models of AM fabricated lattice structures.

Modeling Methods for Collapse Analysis of Reinforced Concrete Frames with Infill Walls

Progressive collapse behavior of RC infilled frames is studied experimentally under quasi-static loading and numerically by using macro (strut) and micro (finite-element) models to simulate the damage propagation within infill walls. A three-strut model is proposed to simulate the overall behavior of infill walls based on the observation that corner regions of infill walls play an important role even after the cracking of the diagonal region in infill walls. The proposed three-strut model is implemented using commercially available software. The accuracy of the proposed method is evaluated by comparing the experimental data with simulated responses from detailed finite-element models and simplified strut models. The modified three-strut model is also compared with other widely used strut models. The comparison shows that the proposed three-strut model predicts the maximum resistance force with higher accuracy. Finally, a simpler model is developed based on the proposed three-strut model for infill walls. This simpler model can easily be implemented by practicing engineers to predict the overall behavior of the infilled frame with acceptable accuracy.

Research on Improved Equivalent Diagonal Strut Model for Masonry‐Infilled RC Frame with Flexible Connection

The reinforced concrete (RC) frame with masonry infill wall is one of the most common structural systems in many countries. It has been widely recognized that the infill wall has significant effects on the seismic performance of RC frame structure. During the Wenchuan earthquake (China 2008), a lot of infilled RC frame structures suffered serious damages due to the detrimental effects brought about by the infill wall rigidly connected to the surrounding frame. In order to solve this problem, flexible connection, introduced by Chinese designers, is recommended by the updated Chinese seismic design code, because of its effect to reduce the unfavorable interaction between infill wall and frame. Although infilled RC frame structure with flexible connection has a lot of advantages, but because of the lack of research, this structure type is seldom used in practical engineering. Therefore, it is of great significance to scientifically investigate and analyze the effects of flexible connection on structure behaviors of infilled RC frame. In this study, a macrofinite element numerical simulation method for infilled RC frame with flexible connection was investigated. Firstly, the effects of connection between infill wall and surrounding frame on in‐plane behaviors of infilled RC frame were discussed. Secondly, based on deeply studying the equivalent diagonal strut models for infilled RC frame with rigid connection, an improved equivalent diagonal strut model for infilled RC frame with flexible connection was proposed. Employed with inversion analysis theory, the parameter in the proposed model was estimated through artificial fish swarm algorithm. Finally, applied with the existing experiment results, a case study was conducted to verify the effectiveness and feasibility of the proposed model.

Simplified macro-modelling strategies for the seismic assessment of non-ductile infilled frames: a critical appraisal

Reinforced concrete frames (RCFs) represent the most widespread structural typology in several high-seismic regions worldwide. Two categories of buildings can be distinguished: modern buildings designed following a specific seismic code and existing buildings designed only to resist to gravity loads. In both cases, the structural response of RCF may be positively or negatively conditioned by the non-structural masonry infills. Neglecting the infills in the analyses can produce an unsafe prediction of the seismic performance of a structure. In contrast, simplified modelling approaches are needed in current engineering practice, since rigorous modelling strategies, namely non-linear finite-element models, are generally incompatible with the standard hardware/software adopted by practitioners. In this paper two macro-modelling approaches, namely the equivalent diagonal strut model and a recently introduced 2D discrete macro-model, which are currently employed by engineers for predicting the seismic behaviour of infilled frames, are compared. The aim of this investigation is to highlight the influence of the modelling approach and calibration procedures on the seismic performance assessment of infilled frame structures. A recent experimental study on a 1-bay infill frame prototype and a multi-storey frame are considered as benchmark cases. The results obtained highlight the differences between the two approaches in terms of capacity curves and collapse mechanisms.

Analytical Validation of Macromodeling Techniques of Infilled RC Frames

The present study focuses on validation of compressive strut models, in which infill wall is replaced with single and multi-equivalent diagonal struts. A full-scaled, one-bay and one-story reinforced concrete (RC) frame, representing weak sides of existing buildings widely used in Turkey, is produced and tested under lateral cyclic loading. Furthermore, the efficiency of three different strut models, commonly used in the literature to present the effects of walls on the RC frames, is investigated using finite element method. Consequently, the analytical results show that single equivalent strut model is an easy and influent way of representing global behavior of infilled RC frames. Additionally, using multi-struts will only cause small variations in global behavior of the system, whereas the failure mode of the RC frame is more accurately represented compared to single strut.

Probabilistic seismic demand assessment accounting for finite element model class uncertainty: Application to a code‐designed URM infilled reinforced concrete frame building

SummaryReliable and robust probabilistic assessment of structures requires explicit consideration of all relevant sources of uncertainty, both aleatory and epistemic. This paper proposes a formulation to incorporate model class uncertainty in probabilistic seismic demand assessment (PSDA) of structures, where model class uncertainty relates to the use of different structural analysis models used to predict the physical response of structural systems. The application of the proposed formulation is illustrated through the assessment of a recent code‐designed reinforced concrete (RC) frame building with unreinforced masonry (URM) infills, which is a prevalent form of construction worldwide. The model class uncertainty analyzed in this paper is related to the potential selection of one of three state‐of‐the‐art masonry infill strut models. In the application example, nonlinear static pushover (NSP) analyses and tornado sensitivity analyses are performed to identify the important parameters of infill strut models affecting the seismic response of the infilled RC frame. A hybrid stripe analysis (HSA) approach is adopted to perform nonlinear response history analyses (NRHAs) of the example RC frame. To account for relevant sources of uncertainty, latin hypercube sampling (LHS) is used to quantify the minimum number of realizations of model parameters necessary to achieve convergence of the coefficient of variation (COV) of the engineering response parameters assessed. Results of the NRHAs indicate that incorporating model class uncertainty significantly affects the estimation of uncertainties of the drift hazard demand.

Robust Calibration of Macro-Models for the In-Plane Behavior of Masonry Infilled RC Frames

ABSTRACT Masonry-infilled reinforced concrete (RC) frames are a widely adopted building system. Although usually disregarded in design, masonry infills are known to affect the behavior of structures under earthquake loading. Adequate numerical models are therefore required to perform realistic analyses of their behavior under earthquakes. In this context, macro-models are known to be efficient tools for this purpose but their properties need to be calibrated using adequate data and procedures to obtain realistic results. In light of this, procedures to calibrate and define the main parameters of different types of macro-models representing the behavior of masonry infills are proposed. The calibration procedures are first presented for the case of single strut models and are then extended for macro-models with different configurations. The validity and performance of the procedures are then tested for several case studies using experimental data from different RC infilled frame specimens.

Micro and Macro-modeling Techniques for the Simulation of the Masonry Infilled R/C Frames under Earthquake Type Loading

Three types of numerical simulation techniques for the masonry infills are adopted in the current paper, namely a micro-modeling technique, a macro-modeling technique and a simulation where the masonry infill and the joint interface between the surrounding frame and the infill is represented by a diagonal strut model. Initially, the hysteretic behavior of three R/C frames with masonry infills tested at the Laboratory of Strength of Materials and Structures of the University of Thessaloniki are examined when they are subjected to horizontal cyclic loads. Non-linear finite simulations are employed, that can describe the reduction of strength and initial stiffness. The inelastic behavior of the frame is simulated including the non-linear simulations of the masonry infill, the formation of plastic hinges for the R/C frame at pre-defined locations and the sliding or the separation of the masonry infill from the surrounding R/C frame. The second part of the present work examines the effectiveness of the micro-modeling technique and that of the diagonal strut model for the numerical simulation of masonry infills inside R/C frame specimens when different types of openings are considered. The results from three framed masonry infill specimens that were tested under horizontal cyclic loading at the University of Osijek have been also utilized for the validation of the micro-model technique and the diagonal strut model that is proposed. Differences and similarities between the adopted numerical modeling techniques are commented and discussed.

Micro and Macro-modeling Techniques for the Simulation of the Masonry Infilled R/C Frames under Earthquake Type Loading

Three types of numerical simulation techniques for the masonry infills are adopted in the current paper, namely a micro-modeling technique, a macro-modeling technique and a simulation where the masonry infill and the joint interface between the surrounding frame and the infill is represented by a diagonal strut model. Initially, the hysteretic behavior of three R/C frames with masonry infills tested at the Laboratory of Strength of Materials and Structures of the University of Thessaloniki are examined when they are subjected to horizontal cyclic loads. Non-linear finite simulations are employed, that can describe the reduction of strength and initial stiffness. The inelastic behavior of the frame is simulated including the non-linear simulations of the masonry infill, the formation of plastic hinges for the R/C frame at pre-defined locations and the sliding or the separation of the masonry infill from the surrounding R/C frame. The second part of the present work examines the effectiveness of the micro-modeling technique and that of the diagonal strut model for the numerical simulation of masonry infills inside R/C frame specimens when different types of openings are considered. The results from three framed masonry infill specimens that were tested under horizontal cyclic loading at the University of Osijek have been also utilized for the validation of the micro-model technique and the diagonal strut model that is proposed. Differences and similarities between the adopted numerical modeling techniques are commented and discussed.

Shear behavior of RC interior joints with beams of different depths under cyclic loading

Extensive reinforced concrete interior beam-column joints with beams of different depths have been used in large industrial buildings and tall building structures under the demand of craft or function. The seismic behavior of the joint, particularly the relationship between deformation and strength in the core region of these eccentric reinforced concrete beamcolumn joints, has rarely been investigated. This paper performed a theoretical study on the effects of geometric features on the shear strength of the reinforced concrete interior beam-column joints with beams of different depths, which was critical factor in seismic behavior. A new model was developed to analyze the relationship between the shear strength and deformation based on the Equivalent Strut Mechanism (ESM), which combined the truss model and the diagonal strut model. Additionally, this paper developed a simplified calculation method to estimate the shear strength of these type eccentric joints. The accuracy of the model was verified as the modifying analysis data fitted to the test results, which was a loading test of 6 eccentric joints conducted previously.

Effect of Masonry Infill Wall Configuration and Modelling Approach on the Behaviour of RC Frame Structures

The masonry infill walls influence substantially the response of reinforced concrete (RC) buildings under lateral loading due to their contribution to strength and stiffness. In the literature, there are several approaches for modelling the infill walls. However, they provide different results. In this study, the equivalent diagonal strut model was used. The basic parameter of this strut is its equivalent width. In the first stage of the study, various equations available in the literature for determining the width of the compressed diagonal strut were compared. Among them, Paulay and Priestley relation which gives approximately average value was selected for modelling the masonry infill walls. In the second stage of the study, a sensitivity analysis was performed by considering 2-, 4-, 6- and 8-storey RC bare frames and those with infill walls. Four different infill wall frame configurations, namely fully infilled frame, fully infilled-except first storey frame, interior bay infilled frame and interior bay infilled-except first storey frame, were adopted. Single-strut and three-strut models for simulating wall panels were used in all infilled frames. Thus, a total of 36 different RC frame models were evaluated through the nonlinear pushover analysis in order to appraise the infill wall effect on the overall response of the case study frame buildings. The analysis of the results indicated that the arrangement of the infill panels over the elevation of the frame remarkably influenced the performance of structures. Moreover, the serious capacity degradation was observed especially for the case of infills discontinued at the ground level.

Effect of Steel Fiber Ratios on Behavior of High Strength Hybrid Reinforced Concrete Deep Beams under Repeated Loading

Introduction: The present work presents experimental and analytical investigation of the effect of steel fiber ratio of behavior of high strength hybrid reinforced concrete deep beams under monotonic and repeated two point load. Methods: The experimental work included casting and testing of six deep beams, three of which were tested under monotonic loading (control beams) and other beams were tested under repeated loading at level of 75% of ultimate load of control beams. The effect of different SF ratios (0%,1% and 2%) with constant amount of web reinforcement (pw) were studied in terms of crack patterns, ultimate load and load versus mid span deflection. Results and Conclusion: From the experimental test results, it was observed the percentage increase ultimate load for hybrid beam cast with SF ratio 1% is 9.62% as compared with hybrid beam with SF ratio 0%. Also, the ultimate load for hybrid beam cast with SF ratio 2% is 28.85% as compared with hybrid beam with SF ratio 0% and 17.54% as compared with hybrid beam with SF ratio 1% under monotonic loading. Strut and Tie Model (STM) procedures were used to analyze the experimentally tested hybrid deep beams under monotonic loading of the present investigation.

A numerical procedure for modeling the floor deformability in seismic analysis of existing RC buildings

In the paper is presented a research study on floor system behavior in existing Reinforce Concrete (RC) buildings under horizontal actions. Generally, vulnerability analysis consists in the study of effective structural behavior of buildings, in order to carry out the assessment, comparing seismic demand and structural capacity. To this purpose, the hypotheses at the base of Finite Element (FE) numerical model, as rigid floor assumption, assume a primary role for the accurateness of seismic analysis results.In the study, after carrying out a preliminary assessment on significant parameters, which influence the floor stiffness, a new numerical simplified procedure has been proposed. Starting by micro-models, made with solid elements, on several simple applications, the behavior of floor system in elastic field has been analyzed in terms of in-plane displacements and a thickness of an equivalent shell of orthotropic material has been defined, usable in macro-model of frame-shell elements.Subsequently, using the procedure proposed, a real case of existing RC buildings has been investigated. The results of linear analysis have been evaluated through their comparison with those obtained by a model where the flexibility of slab is simulated with a more consolidate method like “strut model”.The numerical analyses carried out have enabled to give interesting indications about both the accuracy of rigid floor assumption and assessment of slab elements.

Reinforced Concrete Corbel’s Behavior using Strut and Tie Model

Reinforced concrete (RC) corbel is one of a disturbed region of elements of the structure. SNI 2847: 2013 as a guideline from Ministry of Public Works provides the design of RC corbels by the conventional method and with Strut and Tie Model (STM). The aim of this study is to determine and compare the behaviors of corbels experimentally that designed with both methods. The testing was conducted on two series of specimens and each series consisted of two specimens. Group 1 was designed using conventional method while group 2 designed using Strut and Tie Model. The axial column was tested under 50 kN fixed axial loads and corbels was tested under monotonic loads gradually increased up to failure. The results showed that with the provided steel and compressive strength of concrete, the shear capacity using the conventional method by analysis and experimental respectively were 363.164 kN and 345.7 kN, while the shear capacity using Strut and Tie Model by analysis and experimental respectively were 306.953 kN and 299.35 kN. The shear capacity of specimens using conventional method was 13.40 % greater than by using Strut and Tie Model and the shear capacity for each conventional and STM method were 1.9232 and 1.6653 greater than designated load.

In-plane response of masonry infill walls: Comprehensive experimentally-based equivalent strut model for deterministic and probabilistic analysis

It is widely recognised that the presence of infills modifies the global structural response of frame buildings subjected to seismic loads. Despite the substantial research carried out in the last decades, the assessment of the seismic performance of infilled frames remains an open issue due to the complexity of the interaction between the infill and the frame and to the large number of parameters involved. In this study, a data set of 162 experimental tests available in the literature is initially employed to assess the reliability of different models based on the equivalent strut approach. The comparison between predicted and experimental values highlights large uncertainties, especially for the stiffness prediction. A novel model is thus developed, that duly takes into account these uncertainties. The constitutive model is piecewise-linear, where characteristic force–displacement points are clearly defined and the related error terms are estimated. Beside the masonry mechanical characteristics, the model considers different features, such as the presence of vertical or horizontal hollows in the units. An example of application of the proposed model is finally presented. Specifically, the cyclic response of experimental tests not included in the original data set is reproduced by making use of the suggested strut model.

Numerical analysis of hydrogen fueled scramjet combustor with innovative designs of strut injector

In this research paper, passive method has been considered to improve the mixing and combustion efficiency of scramjet combustor. Modified and innovative strut injector designs have been developed from the reference of DLR scramjet. Strut is the mechanical component which is placed in the flow stream of supersonic airflow and used to inject the fuel. The newly introduced strut injector models are named as rocket and double arrow shape strut injectors. Numerical analysis of computational domains with innovative strut injectors has been carried out by considering the ANSYS – FLUENT 15.0, which is a numerical simulation tool. Shear stress transport model (SST k−ω model) has been considered for turbulence modeling under high speed flows. From the numerical results, it is observed that the compressed air entered into the combustion chamber is at higher pressure than the basic DLR scramjet model and it reduces the ignition delay. It is also found that both the rocket and double arrow strut models increases the boundary layer separation and vortex formation and therefore it enhances the better mixing of fuel and air and finally it improves the combustion efficiency.

An effective simplified model of composite compression struts for partially-restrained steel frame with reinforced concrete infill walls

To resolve the issue regarding inaccurate prediction of the hysteretic behavior by micro-based numerical analysis for partially-restrained (PR) steel frames with solid reinforced concrete (RC) infill walls, an innovative simplified model of composite compression struts is proposed on the basis of experimental observation on the cracking distribution, load transferring mechanism, and failure modes of RC infill walls filled in PR steel frame. The proposed composite compression struts model for the solid RC infill walls is composed of α inclined struts and main diagonal struts. The α inclined struts are used to reflect the part of the lateral force resisted by shear connectors along the frame-wall interface, while the main diagonal struts are introduced to take into account the rest of the lateral force transferred along the diagonal direction due to the complicated interaction between the steel frame and RC infill walls. This study derives appropriate formulas for the effective widths of the α inclined strut and main diagonal strut, respectively. An example of PR steel frame with RC infill walls simulating simulated by the composite inclined compression struts model is illustrated. The maximum lateral strength and the hysteresis curve shape obtained from the proposed composite strut model are in good agreement with those from the test results, and the backbone curve of a PR steel frame with RC infill walls can be predicted precisely when the inter-story drift is within 1%. This simplified model can also predict the structural stiffness and the equivalent viscous damping ratio well when the inter-story drift ratio exceeds 0.5%.

Investigating the effect of infill walls on steel frame structures

Infill walls consisting of materials such as hollow concrete, hollow clay and autoclaved aerated concrete bricks are not only preferred in reinforced concrete buildings but also in steel frame structures. It is a well-known fact that infill walls limit the displacement of frames under horizontal loads. However, they may also bring about certain problems due to being placed randomly in horizontal and discontinuously in vertical directions for some architectural reasons. Moreover, cracks in frame-wall joints are observed in steel frame structures in which ductile behaving steel and brittle behaving infill walls are used together. In this study, the effect of infill walls on steel frames has been investigated. In the steel frame structure chosen for the study, four different situations consisting of different combinations of infill walls have been modeled by using ETABS Software. Later, the pushover analyses have been performed for all the models and their results have been compared. As a result of the analyses done by using the equivalent diagonal strut model, it has been found out that infill walls limit the displacement of steel frames and increase the performance of a structure. However, it has been also determined that in the steel frame structure in which the infill walls have been placed discontinuously in vertical and asymmetrically in horizontal, infill walls may lead to torsional and soft story irregularities. As a result, it is possible to observe cracks in the joints of infill walls and steel frame, the deformation properties of which differ, unless necessary precautions are taken.