Strut Width Research Articles

Seismic behavior of beam-to-column connections with elliptic slit dampers

The rigid steel connections were suffered severe damage because of low rotational capacity during earthquakes. Hence, many investigations have been conducted on the connections of steel structures. As a solution, steel slit dampers were employed at the connections to prevent brittle failure of connections and damage of main structural members. Slit damper is a plate or a standard section with a number of slits in the web. The objective of this paper is to improve the seismic performance of steel slit dampers in the beam-to-column connection using finite element modeling. With reviewing the previous investigations, it is observed that slit dampers were commonly fractured in the end parts of the struts. This may be due to the low participation of struts middle parts in the energy dissipation. Thus, in the present study slit damper with elliptic slits is proposed in such a way that end parts of struts have more energy absorption area than struts middle parts. A parametric study is conducted to investigate the effects of geometric parameters of elliptic slit damper such as strut width, strut height and plate thickness on the seismic performance of the beam-to-column connection. The stress distribution is improved along the struts in the proposed slit damper with elliptic slits and the stress concentration is decreased in the end parts of struts. The average contributions of elliptic slit dampers, beam and other sections to the energy dissipation are about 97.19%, 2.12% and 0.69%, respectively.

Interfacial Energy-Controlled Top Coats for Gyroid/Cylinder Phase Transitions of Polystyrene-block-polydimethylsiloxane Block Copolymer Thin Films.

Block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) can form well-defined sub-10 nm periodic structures and can be used as a template for fabrication of various functional nanostructures. However, the large difference of surface energy between the blocks commonly found in high-χ BCPs makes it challenging to stabilize a useful gyroid morphology in thin film form. Here, we used an interfacial-energy-tailored top-coat on a blended film of a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP and a low-molecular-weight PDMS homopolymer with a hydrophilic end functional group. The top coat consisted of a random mixture of 40% hydrolyzed poly(vinyl acetate)-random-poly(vinly alcohol) (PVA-r-PVAc, PVA40) and PVAc homopolymer. At the optimized top-coat composition, gyroid nanostructures with sub-10 nm strut width were achieved down to ∼125 nm film thickness, which is only 3 times the lattice parameter of the gyroid structure. This is in marked contrast with a mixed morphology of gyroid and cylinders obtained for other compositions of the top coat. Self-consistent field theoretic simulations were used to understand the effect of the interfacial energy between the top coat and BCP/homopolymer blends on the phase transition behavior of the BCP/homopolymer films.

Inherent limitations and alternative to conventional equivalent strut models for masonry infill-frames

Past studies have confirmed that the behaviour of an infill-frame can be remarkably different from that of a bare frame. This becomes specifically critical when the structure is under lateral loads such as wind and earthquake. This paper looks into the fundamentals of the most commonly used analytical method for the analysis of such structures, i.e. equivalent strut modelling. It is shown that even though several equivalent strut models have been proposed since the 1950s, none can be considered as a suitable generic tool to represent the behaviour of all infill-frame structures. It is further demonstrated that not only the total width of strut(s), but also the number and location of strut(s) may vary from one infill-frame to the next. It is also shown that even for the same infill-frame the strut properties change at different drift values. A methodology is proposed to develop an appropriate strut model incorporating the material nonlinearities for any given infill-frame. This methodology requires the analytical results of a primary FE model at a micro level to determine the geometric properties of struts.

Analyzing the Effects of Temperature, Nozzle-Bed Distance, and Their Interactions on the Width of Fused Deposition Modeled Struts Using Statistical Techniques Toward Precision Scaffold Fabrication

Fused deposition modeling (FDM) is currently one of the most widely utilized prototyping technologies. Studies employing statistical techniques have been conducted to develop empirical relationships between FDM process factors and output variables such as dimensional accuracy, surface roughness, and mechanical properties of the fabricated structures. However, the effects of nozzle temperature (T), nozzle-bed distance (NBD), and their interactions on strut width (SW) have not been investigated. In the present work, a two-way factorial study with three levels of T and NBD in triplicates was undertaken. A fixed-effects model with interaction was proposed and remedial measures based on the error analysis were performed to obtain correct inferences. The factor main/interaction effects were all found to be statistically significant (p < 0.05) using analysis of variance (ANOVA). Multiple comparisons were conducted between treatment means using the Tukey's method. A multiple linear regression (MLR) model (R2 = 0.95) was subsequently developed to enable the prediction of SW. The developed MLR model was verified experimentally; by (1) the fabrication of individual struts and (2) the fabrication of single-layer scaffolds with parallel raster patterns. The percentage error between the predicted and observed widths of individually fabricated struts was 3.2%, and the error between predicted and observed SW/spacing for the single-layer scaffolds was ≤ 5.5%. Results indicate that a similar statistical methodology could be potentially employed to identify levels of T and NBD that yield defined width struts using open architecture, personal or commercial FDM setups, and existing/new materials.

Experimental Study of Partially Masonry Infilled Reinforced Concrete Frame under Lateral Loading

The partially infilled frames are considered vulnerable in terms of captive column effect for the events of earthquakes. Many reinforced concrete buildings have been affected due to captive column effects. Experimental study has been done to verify the captive column effect and its failure modes for partially infilled frames and the results have been compared with the ones obtained for a bare frame subjected to lateral loading. The results of experimental study have also been compared with some analytical results and the verification of equivalent strut width proposed by one of the authors has been done. From the experimental point of view, it is understandable that due to lateral loading to partially infilled frames, the damage pattern is diagonal and the failure of column occurs at the column-wall joint at the upper side of the wall. It is also seen that for fifty percent partially infilled frames, the stiffness of bare frame is enhanced slightly, however, the failure in the column during lateral loading indicates that the columns are subjected to high shear due to the presence of partial infill.

Strut-and-tie model for interior RC beam-column joints with substandard details retrofitted with CFRP jackets

A softened strut-and-tie model (STM) is developed for interior reinforced concrete (RC) beam-column joints without any steel hoops in the joint or intermediate longitudinal column steel reinforcement, and discontinuous bottom beam flexural steel reinforcement. The STM model is extended to identical joints retrofitted with Carbon Fiber-Reinforced Polymer (CFRP) composites. The STM model is compared to experiments of two full-scale RC beam-column interior joints, one of which was retrofitted with CFRP composites. Failure modes for the original joint included anchorage failure of bottom steel beam bars, crushing of concrete nodal zones, diagonal joint shear failure, and for the retrofitted joint CFRP laminate delamination and crushing of joint core concrete. The STM model is based on the joint reinforcement details and experimental performance, including column axial load effects and the contribution of CFRP horizontal and diagonal laminates as tension ties. STM model assumptions were verified with strain gauge measurements. The STM model was successful in estimating the ultimate shear strength of the original and retrofitted joints. Recommendations are presented for evaluating the strut width for both original and retrofitted joints that include the quality of the bond of beam steel reinforcement to concrete in the beam-column joint.

Computational Analysis on Stent Geometries in Carotid Artery: A Review

This paper reviews the work done by previous researchers in order to gather the information for the current study which about the computational analysis on stent geometry in carotid artery. The implantation of stent in carotid artery has become popular treatment for arterial diseases of hypertension such as stenosis, thrombosis, atherosclerosis and embolization, in reducing the rate of mortality and morbidity. For the stenting of an artery, the previous researchers did many type of mathematical models in which, the physiological variables of artery is analogized to electrical variables. Thus, the computational fluid dynamics (CFD) of artery could be done, which this method is also did by previous researchers. It lead to the current study in finding the hemodynamic characteristics due to artery stenting such as wall shear stress (WSS) and wall shear stress gradient (WSSG). Another objective of this study is to evaluate the nowadays stent configuration for full optimization in reducing the arterial side effect such as restenosis rate after a few weeks of stenting. The evaluation of stent is based on the decrease of strut-strut intersection, decrease of strut width and increase of the strut-strut spacing. The existing configuration of stents are actually good enough in widening the narrowed arterial wall but the disease such as thrombosis still occurs in early and late stage after the stent implantation. Thus, the outcome of this study is the prediction for the reduction of restenosis rate and the WSS distribution is predicted to be able in classifying which stent configuration is the best.

Seismic Performance Evaluation of Indonesian Existing R/C Building Considering Brick Infill

This paper presents the seismic performance of an existing building in Padang, Indonesia, considering the brick infill effect by applying a developed analytical model. In this model, masonry infill was replaced by a diagonal compression strut which represented distributed compression transferred diagonally between infill/frame interfaces. The infill/frame contact length could be determined by solving two equations, i.e., static equilibriums related to the compression balance at infill/frame interface and lateral displacement compatibility. Consequently, the equivalent strut width is presented as a function of infill/frame contact length. Two calculations of seismic performance of an existing R/C building, with and without considering brick infill, were performed. A distinct difference was identified between the lateral strength of such building with and without infill effects. As the results, the nonstructural brick masonry infill significantly contributed to the seismic performance of the R/C building.

Load capacity of squat RC shear walls by strut-and-tie model

A simplified strut-and-tie model (STM) is established, based on the crack band theory of fracture mechanics for evaluating the lateral load capacity of squat reinforced concrete (RC) shear walls. The load transfer mechanism of concrete is identified by the strut-and-tie action contributed by the web concrete and longitudinal reinforcement of the boundary elements of the walls, whereas that of shear reinforcement is identified by the tie action idealised using a statically indeterminate truss system. The load transfer capacities of the concrete strut and shear reinforcement are driven using the energy equilibrium in the stress relief strip and the crack band zone formed along a diagonal crack. The width of the main concrete strut is determined using the neutral axis depth simplified as a function of the longitudinal reinforcement ratio and the elastic modulus ratio between concrete and reinforcing bars. Predictions made by the proposed model are in better agreement with test results compiled from 150 specimens than those made by other models. The comparison also reveals that other empirical equations provided by ACI 318-14, Wood, and Gulec and Whittaker significantly underestimate the lateral load capacity of squat shear walls, whereas the STM proposed by Siao overestimates the load capacity.

Calculation method for the shear bearing capacity of diaphragm-through connections

This article presents the results of experimental, numerical, and theoretical studies into the shear behavior of panel zone of diaphragm-through connections between concrete-filled square steel tubular columns and steel beams. The current design code does not cover the yield and ultimate shear strengths of such connections in China. Five tee-shaped diaphragm-through connections were fabricated and tested that they comply with the principle of “strong members and weak panel zone.” Three-dimensional nonlinear finite element models were developed to study the shear behavior of the panel zone under low-frequency cyclic loading. Based on the test results, the force transfer mechanism and the effect of different factors on the panel zone shear capacity were analyzed. The width and deformation of compression strut of core concrete were taken into account. A simple manual calculation method was also proposed for evaluating the shear strength of panel zone of diaphragm-through connections. Good agreement was found between theoretical and test results for both yield and ultimate shear strengths for connections.

Fabrication of Cell-Loaded Two-Phase 3D Constructs for Tissue Engineering.

Hydrogel optimisation for biofabrication considering shape stability/mechanical properties and cell response is challenging. One approach to tackle this issue is to combine different additive manufacturing techniques, e.g., hot-melt extruded thermoplastics together with bioplotted cell loaded hydrogels in a sequential plotting process. This method enables the fabrication of 3D constructs mechanically supported by the thermoplastic structure and biologically functionalised by the hydrogel phase. In this study, polycaprolactone (PCL) and polyethylene glycol (PEG) blend (PCL-PEG) together with alginate dialdehyde gelatine hydrogel (ADA-GEL) loaded with stromal cell line (ST2) were investigated. PCL-PEG blends were evaluated concerning plotting properties to fabricate 3D scaffolds, namely miscibility, wetting behaviour and in terms of cell response. Scaffolds were characterised considering pore size, porosity, strut width, degradation behaviour and mechanical stability. Blends showed improved hydrophilicity and cell response with PEG blending increasing the degradation and decreasing the mechanical properties of the scaffolds. Hybrid constructs with PCL-PEG blend and ADA-GEL were fabricated. Cell viability, distribution, morphology and interaction of cells with the support structure were analysed. Increased degradation of the thermoplastic support structure and proliferation of the cells not only in the hydrogel, but also on the thermoplastic phase, indicates the potential of this novel material combination for biofabricating 3D tissue engineering scaffolds.

TCT-438 Outcomes After Bailout Stenting with Absorb BVS or XIENCE: Meta-analysis of Randomized Trials

The Absorb bioresorbable scaffold (BVS) provides comparable 12-month clinical outcomes to Xience everolimus-eluting stents in appropriately sized vessels. Differences in device structure (strut thickness and width) and resorption might impact outcomes in the setting of bailout (unplanned) device

Neutron diffraction measurements of residual stress in additively manufactured stainless steel

Charpy test specimens were additively manufactured (AM) on a single stainless steel plate from a 17–4 class stainless steel using a powder-bed, laser melting technique on an EOS M280 direct metal laser sintering (DMLS) machine. Cross-hatched mesh support structures for the Charpy test specimens were varied in strut width and density to parametrically study their influence on the build stability and accuracy as the DMLS process has been known to generate parts with large amounts of residual stress. Neutron diffraction was used to profile the residual stresses in several of the AM samples before and after the samples were removed from the support structure for the purpose of determining residual stresses. The residual stresses were found to depend very little on the properties of the support structure over the limited range studied here. The largest stress component was in the long direction of each of the samples studied and was roughly 2/3 of the yield stress of the material. The stress field was altered considerably when the specimen was removed from the support structure. It was noted in this study that a single Charpy specimen developed a significant tear between the growth plate and support structure. The presence of the tear in the support structure strongly affected the observed stress field: the asymmetric tear resulted in a significantly asymmetric stress field that propagated through removal of the sample from the base plate. The altered final residual stress state of the sample as well as its observed final shape indicates that the tear initiated during the build and developed without disrupting the fabrication process, suggesting a need for in-situ monitoring.

R/C frame–infill interaction model and its application to Indonesian buildings

SummaryThis paper proposes a new analytical model for masonry‐infilled R/C frames to evaluate the seismic performance considering R/C frame–infill interactions. The proposed analytical model replaces masonry infill with a diagonal compression strut, which represents distributed compression transferred between frame and infill interfaces. The equivalent strut width is presented as a function of the frame–infill contact length, which can be evaluated by static equilibriums related to compression balance and lateral displacement compatibility at the frame–infill interfaces. The proposed analytical model was verified through comparisons with experimental results obtained for several brick masonry‐infilled R/C frames representing a typical R/C building with nonstructural masonry infill in Indonesia. As a result, good agreements were observed between the experimental and analytical values of the lateral strength and ductility of the infilled frames. The seismic performances of two earthquake‐damaged R/C buildings with different damage conditions were evaluated considering infill effects by applying the proposed analytical model. Consequently, the nonstructural brick masonry infill significantly affected the seismic resistances of the buildings, which seemed to lead to differing levels of damage for each building. These results indicate that the proposed analytical model can be an effective tool for more precisely screening earthquake‐vulnerable existing R/C buildings in Indonesia. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.

Experimental Study on Lateral Strength Evaluation of Unreinforced Masonry-Infilled RC Frame

In this study, RC frames with unreinforced masonry (URM) infill for typical school buildings in Korea are experimentally investigated to evaluate their seismic performance. For this purpose, one-bay, one-fourth scale specimens, with unreinforced concrete block (CB) infill having different boundary conditions due to beam rigidity, are tested under in-plane cyclic loading, using a distinctive measurement scheme consisting of three-axis strain gauges attached to all CB units. In this paper, the diagonal strut mechanism of CB infill including its main strut angle, average compressive strain, and equivalent strut width is discussed using principal compressive strains on CB units. The lateral strength carried by CB infill and RC frame from the overall response of the specimens is also explained, based on the compressive stress acting on the infill and the curvature distribution along RC members during the test.

Differential thrombotic prolapse burden in either bioresorbable vascular scaffolds or metallic stents implanted during acute myocardial infarction: The snowshoe effect: Insights from the maximal footprint analysis

BackgroundThe hypothesized increased thrombus entrapment during bioresorbable vascular scaffold implantation in acute myocardial infarction, the so-called “snowshoe effect” has never been demonstrated. MethodsPatients enrolled in the BVS STEMI FIRST study matched with STEMI patients implanted with everolimus-eluting metal stents (EES) and undergoing optical coherence tomography (OCT) at the index procedure were compared. Quantitative coronary angiography analysis and optical coherence tomography data for evaluation of thrombotic prolapse were reported. Percentage maximal footprint (%MFP) analysis as an indicator of the snowshoe effect was performed. ResultsA total of 302 patients were analyzed (151 with BVS and 151 with EES). Of those patients 30 implanted with BVS and 17 implanted with EES were imaged at the index procedure with OCT. Baseline clinical characteristics, TIMI-flow and thrombus burden were similar between groups. Aspiration thrombectomy was similarly performed in the two groups (BVS 83.3% vs 94.1% EES, p=0.405). At the end of the procedure, final TIMI 3 flow was achieved in 93.3% and 82.4% of BVS and EES patients respectively (p=0.296). The %MFP was significantly higher in the BVS treated patients (36.59±5.65% vs 17.61±4.30, p<0.001). The results of the OCT analysis showed a mean prolapse area (0.61±0.26mm2 vs 0.90±0.31mm2, p=0.001) and a percentage prolapse area (7.11±2.98mm2 vs 9.98±2.90mm2, p=0.002) significantly higher in the EES group. ConclusionsScaffold structural characteristics such as strut width may play a role in terms of thrombus dislodgment patterns and acute prolapsing material.

저층형 철근콘크리트 전단벽의 전단강도 평가를 위한 스트럿-타이 모델

The previous strut-and-tie models (STMs) to evaluate the shear strength of squat shear walls with aspect ratio less than 2.0 do not consider the axial load transfer of concrete strut and individual shear transfer contribution of horizontal and vertical shear reinforcing bars in the web. To overcome the limitation of the existing models, a simple STM was established based on the crack band theory of concrete fracture mechanics. The equivalent effective width of concrete strut having a stress relief strip was determined from the neutral axis depth and effective factor of concrete strength. The shear transfer mechanism of shear reinforcement at the extended crack band zone was calculated from an internally statically indeterminate truss system. The shear transfer capacity of concrete strut and shear reinforcement was then driven using the energy equilibrium in the stress relief strip and crack band zone. The shear strength predictions of squat shear walls evaluated from the current models are in better agreement with 150 test results than those determined from STMs proposed by Siao and Hwang et al. Furthermore, the proposed STM gives consistent agreement with the observed trend of the shear strength of shear walls against different parameters.

ANALYSIS OF INFILL FRAME WITH GAP ELEMENTS USING FINITE ELEMENT APPROACH

The rapid urbanisation demands the need of high raised buildings which are always vulnerable to the lateral loads caused due to natural calamities. These lateral loads affect the stability of the structure. The shear walls, which are provided to resist the lateral forces, are not desirable from utility point of view as they come in the way of vehicular movement in the parking floor. In this context the contribution available from wall panels, called infill walls is considered. In this paper, the contribution offered from infill walls to the lateral strength of the building is evaluated using FEM approach. In this approach the infill wall contribution is replaced with two diagonal struts joining the opposite corners of the frame. The general purpose Finite Element package MSC NASTRAN is used to evaluate the infill contribution. Frames with different aspect ratios of span to height with and without wall opening are taken up for the study. On obtaining the strain energy of the infill frame, the infill wall is replaced by equivalent diagonal struts joining the opposite corners of the frame of width to match in strain energy. To make the application more widely applicable, the data obtained from different case studies has been tabulated to train a neural net. The train neural net is expected to offer the width of equivalent strut once the necessary input data is fed. The utility of the study is improved as more data is added.. Later the effect of crack widening in the infill panel was shown by the introduction of gap elements wherever the tensile stress was found more than the permissible value. The failure pattern when a horizontal load, vertical load and rotation each applied in turn at each corner of the infill panel with gap elements is studied

Numerically based proposals for the stiffness and strength of masonry infills with openings in reinforced concrete frames

SummaryAimed at investigating the effect of openings on the in‐plane behaviour of masonry infills in reinforced concrete frames, a parametric study is presented based on model calibration via experimental tests. Two types of openings are investigated: central window openings and different combinations of door and window openings based on the typologies of southern European countries. First, a finite element model of the structure is made using the DIANA software program. Then, after calibration with experimental results, a parametric analysis is carried out to investigate the effect of the presence and location of the different types of openings on the in‐plane behaviour of the infilled frame. Finally, different equations for predicting the initial stiffness and lateral strength of infilled frames with any types of openings were obtained. An α factor related to the geometry of the piers between openings is proposed to take into account the location of the openings in the developed equations. Subsequently, the masonry infill panel is replaced by a diagonal strut. An empirical equation is also proposed for the width of an equivalent strut to replace a masonry infill panel with openings in such a way that they possess the same initial stiffness. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Effect of stiffeners in lateral stiffness of masonry infill reinforced concrete (RC) frames

Infilled frames are reinforced concrete frames with masonry infill. The provision of masonry walls as infill increases the lateral stiffness of frame. Unreinforced masonry infill effects the strength and stiffness of frame but being ignored for a long time. The main objective of this paper is to study the individual and combined effect of infill masonry wall, stiffeners and wooden frame in the lateral stiffness of infill reinforced concrete frame with central opening, with and without gap element consideration. From the analysis using SAP software, it is observed that with increase in openings, stiffness decreases but introducing stiffeners and wooden frame increases the lateral stiffness. Embedding the gap element as the boundary condition reduces the stiffness of the infilled frame. Numerical investigations are carried out by finite element modeling for analyzing the behavior of infilled frame. The single equivalent diagonal strut width was determined by obtaining the same lateral stiffness from finite element model, and also strut reduction factor for different conditions with central openings are proposed.