Prediction Of Failure Modes Research Articles

Effects of end distance on thin sheet steel single shear bolted connections at elevated temperatures

Abstract Thin sheet steel (TSS) single shear bolted connections at elevated temperatures were investigated experimentally in this study. The TSS 0.42 mm G550 and 1.90 mm G450 were used to fabricate the connection specimens. The connection specimens were designed with the variation of end distance. The specimens were tested at 5 different nominal temperature levels up to 900 °C using the steady state test method. The effects of end distance and temperature on the behaviour of bolted connections were investigated. It was found that the ultimate loads increased with the increment of the end distance up to three times the bolt diameter. Generally, the deteriorations of the connection strengths are in a similar manner to the corresponding material properties at elevated temperatures. The experimental results were compared with the predictions by using the Australian/New Zealand Standard (AS/NZS), European Code (EC3-1.3) and North American Specification (NAS) for cold-formed steel structures. In calculating the nominal strengths of the connections, the reduced material properties of TSS obtained at elevated temperatures were used. Overall, it is shown that the predictions from the AS/NZS, NAS and EC3-1.3 are conservative, with the AS/NZS providing the least conservative and least scattered predictions. However, the reliability analysis showed that the design provisions of the three design specifications are not reliable for the TSS single shear bolted connections in this study, with considerable scope for the development of improved design formulae. Generally, the AS/NZS and NAS could provide accurate predictions of failure modes for TSS connection specimens failed in tearout failure and bearing failure at different temperature levels.

Structural behaviour and design of plywood sheathed cold-formed steel wall systems subjected to out of plane loading

An experimental study was conducted to explore the strength contribution of plywood sheathing boards that are regularly used in the cold-formed steel (CFS) wall panel construction. A series of material tests and 4-point bending full-scale tests were carried out. The testing program includes various key design factors such as sheathing board thicknesses, screw spacings and slenderness of the CFS studs. The test results indicate that the plywood sheathing thickness of 12 mm is sufficient for restraining the lateral torsional buckling (LTB) of the slender CFS studs, which also increased the ultimate moment capacity of the CFS wall panel by a maximum of 150%. However, the improvement in flexural strength varies depending on the local and global slenderness of the CFS wall stud. The spacing between the sheathing-screw connection also significantly influenced the structural contribution of plywood-sheathing. The design calculations were carried out as per the AISI design provisions and latest improvements suggested by the previous research works. The design calculations indicate that the design moment capacity of the CFS wall panel can be increased by a maximum of 48%, and most of the design results are conservative compared to the experimental results. Although, it was found that the modified design provisions of AISI are reliable for the strength predictions, the failure modes predicted greatly varied compared to the experimental results. Therefore, a series of individual sheathing screw connection tests were carried out to discover the key factors that influence the bracing effect of sheathings. On the basis of the results obtained from individual sheathing connection tests, the preliminary modifications that are required for the accurate failure mode predictions are suggested.

A fast and efficient numerical prediction of compression after impact (CAI) strength of composite laminates and structures

Abstract In this paper, an equivalent damage model is proposed to quickly predict the compression after impact (CAI) strength of composite laminates and stiffened panels. Low-velocity impact (LVI) and CAI tests at various energy levels are carried out on laminates. Based on the measured impact damage sizes, the model simplifies the damage area into concentric circles with different stiffness and strength properties by adopting the soft inclusion method. Progressive failure analysis and virtual crack closure technique (VCCT) are used to simulate the intra-laminar and inter-laminar failure of impacted laminates under axial compression in commercial finite element software ABAQUS. The predicted failure modes and CAI strength of laminates are in good agreement with the experiment results from this paper and the literature at various impact energies, which proves the validity of the model. Whilst the numerical model achieves high computational efficiency, the effect of mass scaling on computational efficiency and accuracy is evaluated, which provides a reference for the parameter choice in engineering application. The model is further applied to predict the compressive failure load of the stiffened composite panel with skin bay impact damage as a practical application, showing this modelling approach is also suitable to composite structures.

Simplified nonlinear analysis of reinforced concrete coupling beams subjected to cyclic loading

Reinforced concrete shear walls connected by coupling beams form an efficient structural system to resist earthquake and wind loads in tall buildings. However, the analysis of the effects caused by cyclic loading in this kind of system are not so straightforward. In the present paper, simplified nonlinear analysis using monotonic loading are used in order to obtain the behavior of tested coupling beams subjected to cyclic loading. Numerical results have shown that numerical monotonic loading is able to predict with good precision the yielding and the failure loads of the tested coupling beams subjected to cyclic loading. Both the cracking patterns and the predicted failure modes also followed the experimental behavior, ensuring that monotonic loading may be applied to have a first insight concerning cyclic loading.

Optimization of transversal flow stress and strain and weld seam microstructure analysis in butt-HDPE friction stir welded plates

The paper aims to optimize the characteristic performances of friction stir welding of high-density polyethylene in order to predict failure modes in weld nugget and interfacial zones. Three replicates of a face central composite design are employed to estimate the effects of parameters process, on the transversal flow stress and strain of the seam and to understand root causes, which may lead to structural defects such as the onset of cracks and the seam-base metal rupture. The study findings disclose that maximum responses are obtained when the tool rotation speed is set middle and both the feed rate and the plunged surface are set high. The transversal flow stress of the welded seam is found highly sensitive to the plunged surfaces and at a lesser degree to the rotation speed, whereas, the transversal flow strain of the welded seam is mostly sensitive to the rotation speed and at a lesser degree to the plunged surfaces. For the microscopic analysis, it is shown that at low rotation speed, there exist four structural layers in the transition zone between the seam and the base material giving rise to the formation of a continuous line of cracks that can initiate structure failure.

Evaluation of Design Methods for Prestressed Concrete Members with Stirrups Using a New Traditional Shear Database

Prestressed concrete (PC) is increasingly used nowadays for the construction of structures subjected to higher loads. Shear design of PC members is complicated and ambiguous as there is no rational and universally accepted shear design procedure. A comprehensive shear database of PC members helps researchers to understand the complicated and ambiguous shear design procedure. In the present study code provisions on shear design based on 45-degree truss analogy (IS 1343:2012 and ACI 318-14), Modified Compression Field Theory (AASHTO LRFD Design Specifications), Variable angle theory (EC-2) have been investigated along with newly proposed shear strength equations. A shear database covering the traditional shear failures of PC beams with stirrups has been developed to assess the shear strength and behaviour of PC beams. Out of 683 shear tests available from the literature on PC beams a total of 274 PC beams with stirrups has been investigated to assess the degree of conservativeness and accuracy of shear design code provisions and shear strength equations. Investigations on the shear code provisions with various variables that govern the shear strength show that serious attention should be given to the prediction of the accurate failure modes for the web-shear and flexure-shear critical specimens. The oversimplifications in the new shear strength equations have also been highlighted in the present study.

Flexural Behavior of Lightweight Concrete Beams Reinforced with GFRP Bars and Effects of the Added Micro and Macro Fiber

This study evaluated the effect of macro steel fiber (SF), micro glass fiber (GF) and micro polypropylene fiber (PF) in lightweight aggregate concrete, (LWAC) beams reinforced with glass fiber reinforced polymer (GFRP) bars. Firstly, concrete mixtures with different volume fractions of GF, PF and SF were tested up to compressive strength, then determine the optimum fiber content GF, PF and SF added into LWAC mix by 0.3%, 0.8% and 0.25% by the volume of concrete, respectively. Meanwhile, eight rectangular cross-section beams with 100 mm (width) × 200 mm (depth) × 1500 mm (length) were tested by four-point bending beam test up to the ultimate load. The GFRP bars were used to reinforce all beams. The failure modes, load-deflection behavior, ductility, flexural capacity and energy absorption were compared in the test results. The experimental results shown added fibers into LWAC improved the flexural capacity, ductility and energy absorption also enhanced moment capacity by 10.07% to 110%. The results indicated that failure modes of GF and PF specimens were in good consistency with the ACI 440.1R-06 predicted failure modes, but for SF specimens, only concrete crushing failure modes accrued. At the end step, the correction factor ( ) obtained from calculated of the experimental results with the flexural capacity according to the ACI 440.1R-06 and ISIS design manual No. 3.

Damage model based on gradient property method for simulating the tensile behavior of composite laminates with Variable Angle Tow reinforcement

In this work Tailored Variable Angle Tow (VAT) patches with various layup directions are employed to reinforce open-hole carbon fiber composite laminates and the tensile behaviour of the reinforced laminates is investigated. The relationship between the tensile behaviour of the reinforced laminate and the fiber orientation of the VAT reinforcement is revealed by experiments. Moreover, this paper proposes a multi-scale finite element model to simulate the reinforced laminate under tensile load. The multi-scale model, consisting of a unit cell model and a gradient property model, is designed to characterize the constitutive response of VAT composites with various fiber fractions and gradient properties. The comparison of the simulation and experimental results indicates that the model not only provides accurate computed tensile strength with the deviation less than 6%, but also presents failure mode predictions that in accordance with the experimental results.

Predicting the tensile and compressive failure behavior of angle-ply spread tow woven composites

A meso-scale finite element model is developed to study the progressive failure behavior of angle-ply spread tow woven composites under tensile and compressive loading conditions. The size of representative volume element (RVE) for angle-ply woven composites is determined by comparing the model predictions against tensile and compressive experimental results to identify the RVE size that significantly affects the prediction of deformation and failure modes, due to inconsistencies in the periodic geometric features of the 0/90° layer and the ±45° layer. The validated model is shown to be capable of predicting the effective stiffness, strength and main failure behavior of the woven composite under tension and compression loading. The tensile and compressive failure behavior of spread tow woven composites are systemically investigated based on the numerically predicted stress distribution and damage contours. It was found that the presence of 45° angle-ply could enhance the crack propagation resistance of the woven composite. This study provides a detailed understanding of the failure mechanism and modeling strategy for spread tow woven composites.

Structural Behavior of Digitally Fabricated Thin-Walled Timber Columns

This paper aims to investigate the structural behavior of digitally fabricated thin-walled timber sections with edge connectivity provided by integral mechanical press-fit joints. Experimental, numerical, and analytical investigations have been developed to accurately characterize the press-fit section behavior and their failure modes. Plywood fiber orientation, material thickness, and connection tightness are considered as potential factors that may affect the performance of the press-fit jointing system. Experimental testing of square hollow sections (SHSs) under uniaxial compressive loading showed failure of sections through both conventional crushing and novel pop-off bifurcation failures. Pop-off buckling behaviors were shown to be governed by the integral joint transverse stiffness and its magnitude relative to a critical edge stiffness value. Columns with joint transverse stiffness value less than the critical edge stiffness value exhibited pop-off failures. These joint stiffness values were obtained from testing of unloaded joints and were used to obtain accurate predictions of column failure modes. Joint stiffness values for loaded joints were then predicted with an interpolation model mapping axial strain to a tighter connection tolerance and these were used to obtain accurate estimations for column failure load in most of the tested column types. Comparative investigations showed thin-walled sections with integral joints only to be capable of matching the compressive capacities of glued sections, for instances where crushing governed. Similarly, the weight-specific compressive capacity of timber sections was found to be comparable to thin-walled steel sections when crushing governs.

Effect of Holes Drilled Various Distances from the Edge of Douglas Fir Utility Poles Tested in Bending

Abstract Wood utility poles are one of the most critical components of U.S. infrastructure. In the Pacific Northwest, Douglas fir is the species of wood predominantly used. Douglas fir has a relatively thin band of treatable sapwood surrounding an impermeable, but only moderately durable, heartwood core that is susceptible to internal decay. Historically, through boring has been the most commonly adopted practice for improving the performance of Douglas fir poles. Despite the inclusion of through boring in national utility standards, questions continue to rise regarding through boring. One important question regarding the process is how close to the edge holes should be drilled. The objective of this study was to assess the effects of through boring edge distance on the flexural strength of Douglas fir poles using a combination of full-scale flexural testing of poles as well as finite element analysis (FEA). Full-scale testing of 48 utility poles revealed that drilling holes within 50 or 75 mm of the outer edge of a pole had no significant effect on flexural properties. FEA consistently predicted failure modes and flexural properties after accounting for through boring and knot locations. These models could be improved through more accurate representation of grain around knots and then used to explore the effects of different sizes, species, quantities of knots and checks, and other drilling patterns on strength, and, therefore, would reduce the need for actual physical testing.

Research on Buckling and Post-buckling Characteristics of Composite Curved Stiffened Fuselage Panel under Hoop Bending load

In order to study the buckling, post-buckling and failure modes of composite fuselage structures under circumferential bending loads, innovative four-point bending tests technology was developed and performed on composite curved stiffened fuselage panel (CSFP) specimens with two frame configurations of C-section and Z-section. Meanwhile, the stability engineering analysis and estimation based on plate buckling theory and simplified boundary were carried out, and the finite element (FE) models based on Hashin failure criterion were established to simulate the buckling, post-buckling and failure modes of CSFP specimens. The tests and analysis results show that the buckling modes and failure modes of C-section and Z-section specimens are different under positive bending loads. Specifically, the buckling of C-section specimens firstly occurs in the middle of the frame, then local buckling occurs at both ends of the frame, leading to fracture. For Z-section specimens, only local buckling occurs in the middle of the frame, which directly leads to fracture. By comparing the three methods, the results of FE analysis and engineering calculation are in good agreement with the test results. Among them, the prediction of instability mode and failure mode by FE method is very accurate, and the buckling strain calculated by engineering method can provide a good reference for structural design.

Nonlinear Finite Element Analysis Formulation for Shear in Reinforced Concrete Beams

This study suggests a novel beam-column element formulation that utilizes an equilibrium-driven shear stress function. The beam shear is obtained from the bi-axial states of micro-planes, through matrix condensation and zero vertical traction assumptions. This properly remedies the shear stiffening of a one-dimensional beam-column element, keeping its degrees of freedom to a minimum. For verification of the proposed method, a total of seven shear test results of reinforced concrete (RC) beams were collected from the literature, in which the key variables were the reinforcement ratio, the presence of shear reinforcement, and section shape. The advantages are clearly shown in the shear stresses distributions being accurately described and the global load-displacement relations being successfully obtained and matching well with various test results. The proposed model shows satisfactory descriptions of the monotonic load-displacement response of the RC beams failing in multiple modes that vary from diagonal-tension to flexural-compression. In addition, more accurate and reliable information of sectional responses including sectional shear deformation and stresses is collected, leading to better prediction of a potential shear failure mode. Finally, the advantages of the proposed model are demonstrated by comparing the analysis results of an RCT-beam by using the different shear assumptions that include the constant and parabolic shear strains, constant shear flow, and the proposed shear stress function.

Sensitivity and uncertainty analysis of the vessel lower head failure mode and melt release conditions in Nordic BWR using MELCOR code

Nordic boiling water reactors (BWR) employ ex-vessel debris coolability as a severe accident management (SAM) strategy. Melt release mode into a deep water pool located in the lower drywell is a major source of uncertainty for success of such strategy. The main goal of this work is to identify the major contributors to the uncertainty in prediction of vessel failure mode, timing and melt release conditions in Nordic BWR using MELCOR severe accident analysis code. There is a forest of control rod guide tubes (CRGTs) and instrumentation guide tubes (IGTs) in the lower head of a BWR. Failure of the penetrations is considered in this work along with the gross creep rupture of the vessel lower head. Modelling of penetrations failure in MELCOR code is based on parametric models, allowing a user to select different assumptions, such as temperature threshold for penetrations failure, modelling of penetrations assembly and respective failure modes, mode of solid and liquid debris ejection from the vessel. In this work we perform sensitivity analysis to the MELCOR modelling options and sensitivity parameters in unmitigated station blackout scenario (SBO). Results of analysis suggest that (i) vessel breach due to penetration failure is predicted to occur before creep-rupture failure of the vessel lower head, (ii) the mode of debris ejection from the vessel has the dominant effect on the likelihood of creep-rupture failure of the vessel lower head and debris ejection rate from the vessel.

Use of the Knowledge-Based System LOG-IDEAH to Assess Failure Modes of Masonry Buildings, Damaged by L'Aquila Earthquake in 2009

This article, first, discusses the decision-making process, typically used by trained engineers to assess failure modes of masonry buildings, and then, presents the rule-based model, required to build a knowledge-based system for post-earthquake damage assessment. The acquisition of the engineering knowledge and implementation of the rule-based model lead to the developments of the knowledge-based system LOG-IDEAH (Logic trees for Identification of Damage due to Earthquakes for Architectural Heritage), a web-based tool, which assesses failure modes of masonry buildings by interpreting both crack pattern and damage severity, recorded on site by visual inspection. Assuming that failure modes detected by trained engineers for a sample of buildings are the correct ones, these are used to validate the predictions made by LOG-IDEAH. Prediction robustness of the proposed system is carried out by computing Precision and Recall measures for failure modes, predicted for a set of buildings selected in the city center of L’Aquila (Italy), damaged by an earthquake in 2009. To provide an independent meaning of verification for LOG-IDEAH, random generations of outputs are created to obtain baselines of failure modes for the same case study. For the baseline output to be compatible and consistent with the observations on site, failure modes are randomly generated with the same probability of occurrence as observed for the building samples inspected in the city center of L’Aquila. The comparison between Precision and Recall measures, calculated on the output, provided by LOG-IDEAH and predicted by random generations, underlines that the proposed knowledge-based system has a high ability to predict failure modes of masonry buildings, and has the potential to support surveyors in post-earthquake assessments.

Numerical study using FE simulation on rectangular RC beams with vertical circular web openings in the shear zones

Transverse and vertical openings are usually created in beams made of reinforced concrete (RC) to accommodate the pipes and ducts used in utilities. The decrease in shear strength because of the openings causes problems in current RC beams. This study investigates the impact of various vertical circular web openings alongside the shear-area span of an RC beam on its shear performance. To this end, a model with three finite element (FE) dimensions was developed, primarily for investigating and analyzing the outcome of this case. Using the ANSYS-V15 FE program, 41 beams were analyzed. The findings of the eight investigational beams were compared with results from previously published works. The devised model was tested to ensure its accurate functioning, using outcomes already attained through experiments. The outcomes of the experimental test proved that the newly devised FE model could be used to calculate the RC beams’ shear-load capacity and to accurately predict failure modes. The outcomes revealed that the effect of the vertical-opening diameter on the width of the beam section was greater than the effect of the length of the shear span. Therefore, we concluded that the influence of the opening diameter was greater than the effect of the number of openings.

Machine Learning–Based Failure Mode Recognition of Circular Reinforced Concrete Bridge Columns: Comparative Study

AbstractThe prediction of failure mode of columns is critical in deciding the operational and recovery strategies of a bridge after a seismic event. This paper contributes to the critical need of f...

Comparison of two UHPFRC premixes blast resistance with the commonly used concrete based on the failure mode prediction

This paper presents results of extensive experimental programme which took place in 2019. Two proprietary ultra-high performance fibre reinforced composite materials were tested for their blast (contact and close-in) resistance. In total, twenty-eight specimens were tested. Specimens were loaded with explosive charge of weight of 100 - 1000 g in various distances. All specimens were visually evaluated for the damage extend, failure mode and crack pattern. Results from the experiment were compared to the results available in literature for normal strength reinforced concrete. Results showed that both tested premixes performed better than ordinary mixtures in terms of blast resistance. Difference between tested materials and commonly used mixture are described as well. Finally, both materials were compared from the material properties point of view as well as by their blast resistance performance.

A mechanical design model for steel and concrete composite members with web openings

In web opening regions, a significant share of the global shear force is redistributed from the perforated web of the steel beam to the reinforced concrete (RC) slab. This redistribution leads to vertical forces in the shear connectors close to both edges of the opening and influences the internal forces in the steel beam and the RC slab over a length of approximately three times the opening length a0. The global shear failure in the web opening region is affected by the rather brittle behavior of the concrete and is either characterized by a diagonal shear cracking failure of the RC slab, or a local bending failure at the opening edges, or vertical connector failure (concrete break-out) at the ends of the opening. This paper is intended to clarify the structural behavior of web opening regions and proposes easy-to-use models that make it possible to analyze the local internal forces of each partial beam in a mechanically consistent manner. Based on these models, a novel design procedure is presented, that allows efficient design and dimensioning of web openings as well as prediction of shear resistance and failure mode.

Numerical analysis of damage and failure behavior of concrete

The paper discusses an anisotropic continuum damage model for concrete and its numerical implementation into a finite element program to provide an efficient approach suitable for boundary-value problems analyzing nonlinear concrete behavior. The phenomenological continuum approach is based on kinematic description of damage. Irreversible deformation behavior as well as volume increase of material samples even under compression loading are simulated by a damage strain rate tensor. The elastic constitutive equations are affected by damage strain tensors modeling decrease of elastic material parameters. The numerical procedure is based on the damage predictor–elastic corrector technique and the corresponding consistent tangent modulus is presented. Different experiments have been performed and deformation fields are analyzed by digital image correlation technique. Numerical simulations of the experiments show good agreement of the results and elucidate stress and damage states in the specimens. They allow prediction of failure modes of the tested specimens agreeing well with photographs of fractured cylinders and cubes. They also demonstrate the efficiency and the applicability of the proposed continuum damage model.