Strut Model Research Articles

Seismic performance of mortise-tenon joint in prefabricated platform canopy

To optimize the prefabricated canopy joints, improve the construction efficiency, and enhance the seismic performance of assembly joints, a novel mortise-tenon joint (MTJ) was proposed. To evaluate the seismic performance along the vertical and track directions, two 1:1.5 scaled specimens were tested under low-cycle reciprocated loading. The test results find the hysteretic curves in both directions exhibit the “pinch” effect especially in the vertical direction, indicating the feature of shear slippage. The displacement ductility coefficients were all above 5.0, and the ultimate drift ratios were 4.54% and 5.88% respectively, showing excellent deformation ability and ductility. The parameters, such as the sectional strength ratio, the stirrup ratio of the prefabricated beam, the reinforcement ratio and the cross-sectional area of the enlarged section, were analyzed by the validated finite element (FE) models. The analysis shows as the section strength ratio decreases and the stirrup ratio increased, the seismic bearing capacity improved, while the plastic hinge located on the prefabricated column varied to the prefabricated beam ends. Based on the results, it is recommended the number of longitudinal rebars through the prefabricated beam is 4, the stirrup diameter in the prefabricated beam is 10mm and the the column cap is no less than 400mm. Finally, based on the truss-diagonal strut model, a method for calculating the shear strength capacity of the novel joint was proposed. Compared with the test and FE results, the theoretical equations exhibit good computational accuracy.

Topology-defined bioactive properties of porous Ti-6Al-4V scaffolds produced by laser powder bed fusion

The effect of the design of additively printed Ti porous structures on their bioactive properties is elucidated by in vitro testing. 3D-printed scaffolds with pores defined by several bioinspired triply periodic minimal surfaces as well as by a strut model have been engineered. Cell proliferation, angiogenesis and osteogenesis have been studied with the help of multipotent mesenchymal stromal cells. The elementary unit size and pore design can notably modify bioactive properties of porous structures. The models providing maximal bioactive activity of developed scaffolds are discussed.

RC dapped-end beams with various reinforcement layouts: An experimental investigation

Reinforced Concrete (RC) discontinuity regions (D-regions), such as dapped ends, can represent vulnerable zones in existing RC structures since they can exhibit a brittle failure mechanism. In common design practice, the ultimate strength of D-regions is assessed through Strut and Tie (S&T) models. Current design codes recommend two resistant mechanisms for dapped ends but do not provide information about the identification of steel bars involved in the resistant mechanism when the reinforcement is formed by distributed bars. An experimental campaign on dapped-end beams with various reinforcement layouts, including configurations without diagonal bars or with one or multiple layers of diagonal bars, has been carried out at the Structures and Material Testing Laboratory of the Department of Civil and Environmental Engineering in Florence. Results allow for identifying the influence of different reinforcement layouts on the crack pattern at the Service Limit State (SLS) and on the post-peak response. Both the strain on bars and the crack opening displacements are investigated until failure. The work highlights that layouts with distributed diagonal bars reduce the crack widths at the SLS compared to other configurations, increase the ductility, and allow for the timely detection of damaged dapped ends during in situ inspections.

Dynamic model of the UC San Diego NHERI six‐degree‐of‐freedom large high‐performance outdoor shake table

AbstractThe UC San Diego large high‐performance outdoor shake table (LHPOST), which was commissioned on October 1, 2004 as a shared‐use experimental facility of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) program, was upgraded from its original one degree‐of‐freedom (LHPOST) to a six‐degree‐of‐freedom configuration (LHPOST6) between October 2019 and April 2022. A mechanics‐based numerical model of the LHPOST6 able to capture the dynamics of the upgraded 6‐DOF shake table system under bare table condition is presented in this paper. The model includes: (i) a rigid body kinematic model that relates the platen motion to the motions of the components attached to the platen, (ii) a hydraulic dynamic model that calculates the hydraulic actuator forces based on all fourth‐stage servovalve spool positions, (iii) a hold‐down strut model that determines the pull‐down forces produced by the three hold‐down struts, (iv) Bouc‐Wen models utilized to represent the dissipative forces in the shake table system, and (v) a rigid body dynamic model borrowed from robotic analysis governing the translational and rotational motions of the platen subjected to the forces from the various components attached to the platen. Extensive validation against experimental data shows excellent agreement for tri‐axial and six‐axial earthquake shake table tests. This validated model can be coupled with finite element models of test specimens to study the interaction between the shake table system and the specimens, and it offers potential for enhancing motion tracking performance through off‐line controller tuning or advanced control algorithm development.

The In-Plane Seismic Response of Infilled Reinforced Concrete Frames Using a Strut Modelling Approach: Validation and Applications

Reinforced Concrete (RC) buildings often rely on masonry walls to increase their rigidity and strength, distinguishing them from bare frames. Consequently, the lateral capacity of the RC frames is significantly impacted by the presence or absence of these walls. Numerical models are fundamental to understanding this behavior interaction, but the development of robust simplified models is still scarce. Based on this motivation, the reliability of a simplified numerical modelling approach was examined in this study and compared to several experimental tests. An optimized approach was implemented to determine the strut parameters, rather than relying on existing empirical formulae. The reliability of the initial stiffness, maximum strength, and energy dissipation was studied. From the results, the accuracy of the considered modelling strategy can be observed in different types of masonry elements (strong and weak units) with and without openings. The validated simulation approach reveals that the adopted macro-modelling procedure can accurately represent the behavior of infilled masonry frames. The maximum deviation of the prediction of the initial stiffness and maximum strength was found to be around 23% and 14%, respectively. These findings illustrate that the strut model effectively replicates real behavior with a satisfactory level of accuracy. However, using a consistent formula to define the strut can result in significant errors, particularly in strut width.

The role of annular 2-lobe nozzle in a strut injection system on the mechanism of fuel distribution at a scramjet engine

The strut injection system is a conventional technique for the injection of the fuel in combustor in hypersonic vehicles. The present article investigates the usage of the annular 2-lobe injector to improve the fuel jet behind the strut. Computational studies have been employed for the modeling of fuel jets released from 2-lobe injectors at the supersonic free stream of the combustion chamber. Simulation of the compressible flow is done by solving Reynolds-Averaged Navier-Stokes (RANS) equations with the turbulence model of SST. The roles of the proposed injection configuration on the flow and fuel jet penetration are disclosed in this work. The shape of fuel jet plume behind the injector is also investigated to explain the mechanism of fuel jet distribution in this technique. Presented data disclosed that the usage of the annular 2-lobe nozzle instead of a single circular jet improves fuel mixing by about 50 % behind the strut model.

Aeroacoustic characteristics of a strut-braced high-lift device

The aerodynamic and aeroacoustic performance of a strut-based high-lift device were evaluated and demonstrated for six different strut models. The primary objective of the study was to investigate the impact of strut modifications on reducing noise levels. The aerodynamic characteristics are presented with the aid of surface pressure distribution on the airfoil that remained consistent across all the tested configurations. The aeroacoustic results are presented as the near-field surface pressure fluctuations and far-field noise measurements to attain a profound comprehension of the noise generation mechanism. Although the Albatros strut exhibited the greatest reduction in tonal noise, the directivity pattern and the overall sound pressure level of the radiated noise demonstrated that the medium height strut configuration can achieve noise reduction of up to 8 dB. The near-field unsteady surface pressure measurements are suggestive of harmonic oscillations. The coherence studies carried out have shown a decrease in the tonal coherence for the small height strut configuration while the velocity field measurements performed in the wake of the high-lift device show no significant variation in flow patterns between different strut configurations.

An experimental campaign for assessing the role of tensioned tendons on the shear capacity of half-joints

An important percentage of bridges and viaducts constituting the Italian road infrastructures dates back to the years 50s and 60s and is characterized by prestressed r.c. decks adopting half-joints for obtaining statically determinate schemes. In existing bridges, half-joints are often subjected to degradation phenomena, mostly promoted by water percolation and stagnation, which led to classify the bridge in a high attention class, according to the Italian Guidelines for Risk Classification and Management, Safety Assessment and Monitoring of Existing Bridges. Furthermore, half-joints are difficult to inspect and to maintain. The current safety assessment procedures at ultimate limit state are based on simplified Strut&Tie models that usually neglect the contribution of prestressing tendons anchored in the half-joints on the resisting mechanisms and the ultimate capacity. This work presents the design of an experimental campaign for investigating the shear behaviour and the ultimate capacity of half-joints in which inclined prestressed tendons are anchored. In detail, six laboratory scaled post-tensioned beams are built with half-joints in correspondence of the support regions, dimensioned on the basis of a real bridge girder and numerical 3D finite element nonlinear analyses. The main research goal is to evaluate the influence of tendons on the half-joints capacity by comparing results with those obtained from specimens with non-tensioned tendons and without tendons. Three levels of pre-tensions in specimens characterized by the same reinforcements are considered. In addition, for one level of pre-tension, the effects of different half-joints detailing are investigated. Finally, the role of degradation due to ageing is also addressed by inducing corrosion in one specimen through a galvanic method.

Methods for evaluating the ultimate capacity of existing RC half-joints

Reinforced Concrete (RC) discontinuity regions (D-regions), such as half-joints, can represent vulnerable zones in existing RC structures since they can be affected by a quasi-brittle failure mechanism. In common design practice, the ultimate strength of D-regions is assessed through Strut and Tie (S&T) models. It is well recognized that the resistant lattice trusses suggested by the Eurocode 2 (EC2) and usually adopted in determining the resistance of new D-regions during the design phase, provide results on the safe side. Nevertheless, in existing half-joints, primary reinforcing bars are frequently distributed across multiple layers, which makes it not easy to identify the appropriate S&T model. For instance, the ultimate capacity of these half-joints could be misestimated if distributed bars are replaced by an equivalent tie passing for their centroid, as is typically done in common practice.The present paper provides two analytical methods for identifying the reinforcement bars involved in the resistant mechanism of D-regions and determining the axial forces in all of them. The proposed methods estimate the ultimate shear resistance of existing half-joints. The accuracy of the proposed procedures is checked through a comparison with numerical results. The methods, capable of identifying the weakest component in the resistant mechanisms of RC D-regions, can be adopted for the assessment of the load-carrying capacity of existing half-joints and identify the proper structural strengthening works to increase the ultimate strength and ductility.

Design and Analysis of Beam with Opening using Strut and Tie Model

Concrete beams on structures sometimes have to be covered for utility lines. For the case of concrete beams with openings, special calculations must be made because the lengths of the dimensions no longer have the same dimensions. One of the approaches is with the strut and tie model. Currently, there are no standard provisions in the manufacture of the strut and tie model, as it is an approach to calculating in areas where Bernoulli's law does not apply. In order to facilitate the creation of a strut and tie model, the study used a simple software tool called BESO2D. The number of samples of the test model is 4 variations with different position and size of the hole. The dimensions of the beam used are 150x300 mm with a length of 2000 mm. Each of the beams will be given a reinforced based on the working load and from the strut and tie model frame. The behavior of each beam will be analyzed using the software of the finite element method to specific concrete named ATENA.

Effect of tie column on the progressive collapse performance of infilled reinforced concrete frames

In practice, reinforced concrete (RC) infilled frames having longer span are provided with tie columns to improve structural integrity but previous work ignored tie columns in studying the effect of masonry infills on progressive collapse resistance of RC frames. Therefore, aim of this study is to explore the effect of tie columns on the progressive collapse resistance of RC infilled frames under column removal scenarios. The high-fidelity-based finite element model of RC infilled frames were first developed and validated with published experimental results. The validated model was then further evolved to an RC infilled frame having tie columns to evaluate the influence of tie columns on the load transfer mechanism and the resistance of the RC infilled frame against progressive collapse. Thereafter, the numerical model was further utilized to study the effects of the pertinent parameters, including the number of stories, the span length of the frame and the longitudinal reinforcement ratio of the tie columns. Finally, equivalent strut model was suggested for macro-modeling of RC infilled frames having tie columns in engineering practice. The results showed that incorporating tie columns makes truss mechanism more fully mobilized in masonry infill walls and the inclined angles of primary struts in each sub-panel of the infill wall are increased, improving the vertical components of diagonal compression in resisting the gravity load. Consequently, introducing tie columns at middle span of infill wall panels helped to increase the initial stiffness (about 19%), peak resistance (about 26%) and post-peak resistance of RC infilled frame under a middle column removal scenario. Such beneficial effect of tie columns becomes more significant for infilled frames with larger spans, and the longitudinal reinforcement ratio of tie columns should be ≤ 0.24%.

A Strut and Tie Model for Steel Fiber Reinforced Concrete Deep Beams

A Strut and Tie Model for Steel Fiber Reinforced Concrete Deep Beams

Experimental investigation of the seismic resistance of RC beam–column connections after freeze–thaw cycle treatment

The freeze–thaw cycle (FTC) is one of the major factors leading to damage to reinforced concrete (RC) structures in severely cold regions. The seismic resistance of FTC-damaged RC beam–column connections is critical to the assessment of structural safety. However, studies on the seismic resistance of FTC-damaged RC beam–column connections under severely cold environments are still scarce. In this study, the seismic resistance of FTC-damaged RC connections was investigated in terms of the failure process, hysteresis, energy consumption, core area shear behavior, etc. Furthermore, the effects of FTC action at the microscopic level and macroscopic level and the damage mechanisms of the connections were investigated. The results showed that the shear force ratio of the connections varied via the “diagonal compression strut model” and “truss model” propagation due to the FTC-induced deterioration of the bond performance between the longitudinal rebar and concrete in the beam end; this variation in the shear force ratio, in turn, led to the transformation of the failure mode of the connections. Moreover, as the number of FTCs increased, the ductility of the connections increased slightly, and the shear distortion in the core region as well as its contribution to the whole displacement gradually rose. When the shear–compression ratio is >0.208, increasing the axial force ratio will reduce the load carrying capacity and the shear distortion in the core zone. Based on the test results, a calculation model of the shear force–strain envelope curve of RC connections that integrates the effects of the inhomogeneous temperature field distribution and axial compression ratio was established.

Experimental study and structural analysis of tapered steel beams with cellular openings

As cellular beams are increasingly used in steel construction, different configurations, including tapered cellular beams, are emerging. Steel beams with cellular openings that are tapered have several benefits, as they combine the benefits of an optimally tapered cross-section with practical cellular advantages. To the best of the author's knowledge, the existing literature only contained analytical and numerical studies on tapered cellular beams. Due to the lack of experimental data, an experimental investigation of six tapered specimens with various circular web opening configurations is presented. The geometry of the tested specimens was discussed, and all specimens have narrow web-posts. The tapered cellular I-sections were tested as cantilevers with fixed support and under a vertical concentrated load. Material properties, manufacturing, supports and test-setup were provided. Factors affecting the behavior of the tested specimens, such as taper angles, optimizing the opening diameter and the opening arrangements, were investigated. The results showed that changing the taper angles had an effect on the buckling strength of the investigated beams. In the meantime, optimizing the opening diameter increases the ultimate strength. A structural analysis of a single web-post was presented, and the experimental specimens' web buckling resistance was determined using the simple strut model. The buckling lengths presented in literature were discussed. The results of the analytical methods demonstrated that the change made by Panedpojaman et al. [1] for estimating the buckling strength was visible and more conservative for tapered cellular beams.

Evaluation of collapse resistance of masonry-infilled RC frame building under blast loadings

As non-structural members, the masonry-infilled (MI) walls are always ignored in the numerical and experimental study on the blast and collapse resistance of RC frame buildings, while the contribution of MI walls on preventing the large-scale collapse has been observed according to the past explosion incidents. This paper aims to propose and verify a numerical simulation approach considering the blast- and collapse-resistant effects of MI walls, and further evaluate the collapse resistance of MI RC frame buildings under blast loadings. Firstly, based on our previously validated hybrid finite element (FE) modelling approach for RC frame structures and Multi-material Arbitrary Lagrangian-Eulerian method for applying blast loadings, the simplified micro-model and compressive strut model of the MI wall were adopted to characterize its blast and collapse resistance in the near- and far-regions of building, respectively. Secondly, the out-of-plane explosion test and in-plane quasi-static collapse test were numerically reproduced to verify the applicability of adopted FE modelling approaches for MI walls. Furthermore, by establishing the hybrid FE models of prototype bare and MI RC frame buildings, the propagation of blast waves, damage modes as well as dynamic responses of RC frame buildings under two design-based threat of explosion at corner and side columns were derived and examined. Finally, the applicability of the anti-collapse design method specified by U.S. Department of Defense, i.e., alternate path method (APM), for RC frame buildings under external explosions was examined. It derives that, (i) the presence of MI walls can efficiently block the blast waves into the building structures, and relieve the upward arch of slabs and damage degree of interior columns; (ii) compared with the bare RC frame buildings, the MI walls provide sufficient alternate load paths to enhance the structural robustness and restore the gravity stability of MI RC frame buildings after the explosions; (iii) the APM is only applicable to evaluate the collapse resistance of MI RC frames under the external explosion of cargo van bomb (1814 kg of equivalent TNT) or even less charge weight.

Quantification of the effects of different uncertainty sources on the seismic fragility functions of masonry-infilled RC frames

The presence of masonry infills is known to have a significant effect when assessing the seismic vulnerability of reinforced concrete (RC) structures, and including these elements in the numerical modelling has become imperative. In computationally-intense probabilistic analyses such as those integrated in performance-based earthquake engineering (PBEE) frameworks, the simulation of the masonry infills is often performed using the single strut approach/technique. Despite the advantages of this modelling approach, it can be related to several sources of uncertainty that can impact probabilistic performance results such as fragility functions. In this context, the proposed study examines the effect of the uncertainty associated to the parameters of the strut model representing the infills, and to the definition of global limit state thresholds reflecting the lateral deformation capacity of infilled structures. The study considers RC structures of different sizes and with different infill configurations, and the relative importance of both sources of uncertainty is analysed by comparing fragility functions defined for different limit states. The comparisons are first performed qualitatively followed by a statistical analysis based on the results of several two-sample tests. Results indicate that, depending on the infill modelling options and on the way limit state values are considered, the corresponding fragility functions can be significantly different. These results highlight the need for further research dedicated to the uncertainty quantification and propagation associated with limit state values for infilled structures and with empirical models that provide parameters for simulating the behaviour of infills under earthquake loading.

Numerical study of the seismic retrofitting of masonry‐Infilled RC frames with openings using TRM

AbstractThe seismic retrofitting of existing masonry‐infilled reinforced‐concrete (RC) frame buildings is one major challenge of earthquake risk mitigation. In this paper, the use of promising novel alternative composite material, namely textile reinforced mortar (TRM) for seismic retrofitting masonry‐infilled RC frames with central openings is examined numerically, to the best knowledge of the authors, for the first time ever. This is achieved by performing a parametric study on a validated 2D numerical model of a three‐story masonry‐infilled RC frame with and without TRM considering different size of central openings. This parametric study aims to examine (i) the influence of central openings on the lateral response of masonry‐infilled RC frames subjected to cyclic loading and (ii) the lateral response of the three‐story masonry‐infilled RC frame with central openings retrofitted with TRM under cyclic loading. From the results obtained in this study, it was concluded that TRM contributes to increase the lateral capacity, stiffness, and the dissipated energy of infilled frames with openings and at the same time provides a more ductile behavior by delaying the strength and the stiffness degradation of infilled frames due to openings and further by delaying or even preventing brittle failures that occur on infilled frames due to the presence of the opening. New stiffness reduction factors for infilled frames with openings, and for TRM‐retrofitted infilled frames with openings are also proposed, which can be used with an equivalent compression strut model and with a tension tie‐model as an everyday practice tool for simulating infilled frames with central openings along the diagonal of the infill wall with and without TRM. A numerical sensitivity analysis is also performed aiming to investigate the influence of (i) the TRM reinforcement ratio and (ii) the type of mortar used for binding the textile reinforcement on the lateral response of the three‐story masonry‐infilled RC frame retrofitted with TRM subjected to cyclic loading. This study showed that by increasing the reinforcement ratio, or by using high‐strength mortars for binding the textile reinforcement, the lateral capacity of infilled frames is increased leading to a more ductile behavior, but this increase is not proportional to the increase of the reinforcement ratio or to the increase of the mechanical properties of the mortar.

Analytical study on behaviour and performance of infilled frame structure with reinforced eccentric opening

This numerical analysis has discussed the behaviour of the frame structure with eccentric infill wall opening modelled with shell and strut elements. In the beginning, validation models were created by following the laboratory tests results. Then, a simple one-storey infill frame structure with an opening was modelled with varying ratios by taking the strut angle formed to obtain an equation for the strut width that corresponds to the behaviour of shell element model with strut angles variation. The strut width equation was then applied to the 3-storey infill frame structures. The behaviour comparison between the strut and shell element model was then investigated by linear and nonlinear static analysis. The strut width equation for infill wall frame with eccentric openings (Weo) is determined by modifying the stiffness coefficient (Ce) based on the opening ratio. The application of the Weo equation to the infill frame model showed that the strut model had a comparable behaviour to the shell element model. The drift ratio comparison showed that the smaller the strut angle, the greater the structure stiffness. The pushover analysis shows the infilled frame model was able to withstand a larger base shear force than the open frame model.

Experimental Study to Evaluate Antisymmetric Reinforced Concrete Deep Beams with Openings under Concentrated Loading Using Strut and Tie Model

Experimental Study to Evaluate Antisymmetric Reinforced Concrete Deep Beams with Openings under Concentrated Loading Using Strut and Tie Model

Fragility models for RC frames with masonry infills and analysis of the efficiency of different IMs

The Italian territory is historically known as a seismic zone, but insufficient attention to seismic design in the past years has led to a high vulnerability of the existing building stock. Fragility models have become important tools for assessing the seismic vulnerability of existing buildings. This work aims to contribute to the assessment of fragility models for reinforced concrete (RC) frames with masonry infills. Based on an analysis of census data on existing buildings and on AeDES forms following the 2012 earthquake in Emilia, a representative 4-storey RC building was defined and modelled with finite elements. A concentrated plasticity approach has been adopted and infill panels have been schematized through an equivalent strut model. Structural capacity has been determined conducting a series of pushover analysis, considering the uncertainties in the mechanical characteristics by means of a Latin Hypercube Sampling. Displacement demand has been evaluated through a multi-stripe non-linear dynamic analysis on the equivalent single degree of freedom systems, by using a set of recorded accelerograms. Fragility curves have been evaluated by means of a regression model on the exceedance of each damage state, defined according to the EMS-98 scale. Particular attention was given to comparing the efficiency of various ground motion Intensity Measures (IMs) in correlating with displacement demand and in describing damage evolution in the building.