Collapse Load Research Articles

The influence of the elastic modulus on the finite element structural analysis of masonry arches

Given the importance of geometry in structural analysis of masonry arches, and taking into account the relationship between stress and deformation, this article presents the influence of the elastic modulus in the collapse mechanism and load for the more common geometries within the masonry arches, considering the effect of the rigidity in the numerical convergence, and the computational cost, within the ABAQUS finite element software. For this, four geometries subjected to ten different elastic modulus are analyzed.The results obtained by the ABAQUS Finite Element Software are compared with the software based on the rigid blocks theory, LimitState Ring.

The mechanical compression performance of ultra-fine grained stainless steel pyramidal lattice core

Severe plastic deformation (SPD) techniques are prospective ones having ability for desirable high mechanical properties to be achieved without any chemical change in metals. Equal-channel angular pressing (ECAP), one of SPD techniques, was used to obtain ultra-high mechanical compressive response of stainless steel pyramidal lattice core. For this purpose, the stainless steel 304 L samples were processed by ECAP at 500 °C. Then, it was sliced into struts and built lattice core after bending processes. At the compression tests, the ECAP lattice core has huge mechanical properties, at nearly two times collapse load and energy absorption values.

The use of Eulerian finite element method in face stability analysis of shield tunnels in undrained clay

This article reports the application of the Eulerian FE method in face stability analysis of shield tunnels in undrained clay. Numerical simulation was first conducted under the total stress framework to verify the accuracy of the approach. Then it was extended to effective stress analysis combined with a critical state model, taking complex behaviours (small strain non-linearity) of soil into consideration. The predictions under the two analysis frameworks were compared in detail, which indicated the small strain formulation of the effective stress constitutive model does not influence the solution for the collapse load but may enhance the predictions of deformation.

Structural Reliability Assessment of Corroded Tanker Ship Based on Experimentally Estimated Ultimate Strength

Abstract This work deals with the reliability assessment of a tanker ship hull structure subjected to a vertical bending moment and corrosion degradation. The progressive collapse and ultimate load carrying capacity are estimated based on experimentally tested scaled box-shaped-specimens. The translation of the strength estimate of the scaled specimen to the real tanker ship hull structure is performed based on the dimensional theory developing a step-wise linear stress-strain relationship. The load-carrying capacity is considered as a stochastic variable, and the uncertainties resulted from the scaled-specimen to the real-structure strength translation, and the subjected load of the real ship are also accounted for. A sensitivity analysis concerning the stochastic variables, included in the ultimate limit state function is performed. The partial safety factors, in the case of a scaled specimen and real structure, are also identified, and conclusions are derived.

Bearing capacity of strip footings on layered sands

In this paper we investigate the bearing capacity of strip footings resting on the top of a relatively thin layer of dense sand, which overlays a weaker sand layer. We use the Finite Element Limit Analysis method to calculate the collapse load and identify the geometry of the failure mechanism, as well as how this geometry changes with varying problem parameters. Results are benchmarked against published experimental data and methods used in practice for the design of working platforms for tracked plant, based on the punching shear model. The observed discrepancies are attributed to the development of a transitional mechanism when the bottom layer is rather dense, and the increase in the shear strength at the interface of the two layers is not abrupt. To cover this gap, we propose a new factor to calculate the bearing capacity in cases where a transitional mechanism will govern failure of the footing.

Optimum first failure load design of one/two-core sandwich plates under blast loads, and their ultimate loads

We consider a sandwich plate with face sheets made of unidirectional fiber-reinforced composite with fibers being either glass, or carbon or aramid and the core made of balsa wood loaded by a blast pressure, and find optimal geometries and materials for maximizing the first failure load. While analyzing the problem, we assume that the areal density is fixed and use the Nest-Site Selection optimization algorithm, a third-order shear and normal deformable plate theory, a one-step stress recovery scheme, and the Tsai-Wu failure criterion. We also delineate the effect on the first failure load of inertia forces and uncertainties in values of various parameters. For a sandwich plate optimally designed for the first failure load, we find the ultimate load by progressively degrading elasticities of failed elements. We find that the optimal single-core sandwich designs are symmetric about the mid-surface with thick face sheets and the optimal two-core sandwich designs have a thin middle face sheet, and thick top and bottom face sheets. The first failure load of the optimal clamped single-core (two-core) design is approximately 20% (30%) more than that of the corresponding simply-supported plate. For simply-supported (clamped) sandwich structures, the failure initiates at the centroid (center of the clamped edge) of either the top or the bottom surfaces. It is also found that the first failure occurs in a face sheet (core) due to the in-plane transverse axial stress (transverse shear stress) exceeding its critical value. The collapse load of a clamped (simply-supported) sandwich structure is approximately 15%–30% (0%–17%) higher than the first failure load. The maximum deflection of the collapsed structure may be in a direction opposite to that of the applied load. A novelty of the work is in considering inertia effects in ascertaining the first and the ultimate failure loads and quantifying the benefits, if any, of two-core over one-core sandwich structures, and determining effects of uncertainties in values of parameters.

Parametric analysis of collapse load factor of planar frames

The plastic analysis and determining the collapse load factor (CLF) of frames have received much attention in all kinematical methods applied for designing these frames. CLF in frames depends on many effective parameters such as length of the bay, the height of story, loads, and plastic moments. As the number of these parameters increases, the analysis becomes more complex and time-consuming. In this regard, artificial neural networks (ANNs) have been found many applications in prediction and optimization of ill-defined problems. In the present paper, two planar frames were considered and analyzed as examples for modeling via ANN. In order to develop the ANNs, results of thirty samples were gathered from every two examples. Parameters including the length of the bay, the height of story, loads, and plastic moments were regarded as inputs and the CLF was considered as the output of the networks. After developing the networks, the model function was generated and the effects of the input parameters were investigated on the CLF of frames. The results showed tuning networks are finely and adjusting their parameters would lead to very good and acceptable results for the design of frames.

COLLAPSE AND BUCKLING OF STAINLESS STEEL PRESTRESSED STAYED COLUMNS

Buckling and collapse of stainless steel elements loaded in compression are studied experimentally and numerically. Based on four tests of single crossarm stayed columns the numerical analysis using ANSYS software package is validated and presented in a detail. First, for a completeness, the study refers to columns with one central crossarm, but the main emphasis is devoted to columns with two crossarms located in the thirds of the element length. The analysis employed geometrically and materially nonlinear analysis (GMNIA) to respect a change of inner energy during buckling of an "ideal" (perfect) column, initial deflections of an "imperfect" column (covering various initial deflection modes and amplitude values) and nonlinear stress-strain relationship belonging to stainless steel material. The results cover both critical buckling and maximal collapse loads of the columns in compression. Finally, the important comparisons of the load capacities concerning stayed columns in compression with one/two crossarms and ratios of critical/maximal loadings, elastic/inelastic material and fixed/sliding support of the stays at the crossarms are provided. Conclusions comprise evaluation of these results and principal recommendations for the design of stayed columns.

Optimization of plastic analysis of moment frames using modified dolphin echolocation algorithm

The analysis of structures and, in particular, the determination of their failure mode are the basic requirements in the field of civil engineering. Obtaining this information in high-rise structures or structures with complex irregular layouts is a difficult process, which even with the use of specialized computer software is very time-consuming. In recent years, meta-heuristic algorithms have been used extensively in engineering optimization problems. This research presents an automated approach to assess plastic loads and failure modes of two-dimensional frames, in which the plastic analysis of moment frames has been optimized using the modified dolphin echolocation optimization algorithm. This method is based on the creation of the basic collapse mechanisms, which, following their combination, should reach the minimum coefficient of plastic collapse loads using virtual work theory. The efficiency of this algorithm is verified using four sample frames, which, their exact solution including minimum load factor and the corresponding critical failure mode of the structure, exit in other research. Comparison of the results shows that the proposed method provides very good results with high precision and speed and also demonstrates the failure mechanism of the structure. Meanwhile, the modifications made in this method have greatly reduced the volume of calculations. Moreover, applying changes to the dolphin echolocation optimization algorithm led to the use of this optimization algorithm for binary problems for the first time, which ultimately resulted in a good convergence rate.

Damage assessment of reinforced concrete flat slabs through modal tests using impact excitation

Purpose In reinforced concrete (RC) structures, an evidence of damage is the presence of cracking. In order to evaluate the effect of damage on cracking pattern and natural frequency in RC slabs, two of such structures with different dimensions and reinforcement ratios were tested, in which cracks were induced through application of static load, followed by modal tests using impact excitation. The paper aims to discuss this issue. Design/methodology/approach The gradient of the fundamental natural frequency along the decay, the crack opening rate and also a global damage index based on changes of the fundamental natural frequency were evaluated. Findings The behaviour of the aforementioned gradient was distinct for both slabs, increasing monotonically with the cracking level for the slab with lowest reinforcement ratio, and increasing until 33 per cent of the collapse load and then decreasing afterwards for the slab with the highest ratio. Changes of the gradient were consistent with changes of the crack opening rate. Both results of gradient changes and cracking pattern brought evidence that the balance between open (old) and breathing (new) cracks differed between the slabs, and may be responsible for such differences. Originality/value Damage assessment in RC structures using vibration tests is mostly concentrated on beams. In this work, an advance is made by investigating slabs. The lack of a unique pattern of changes of the gradient implies that its absolute value is not generally suitable for the association with the damage level. However, the impact tests can be effectively used to detect early damage on slabs using this proposed parameter.

Numerical analysis of collapse load and specific strength for moderate-walled Ti6Al4V-laminate composite submersible vessel under external hydrostatic pressure

The effects of geometrical imperfections on the collapse load and specific strength of moderate-walled submersible vessel made of Ti6Al4V-laminate composites and Ti6Al4V alloy, respectively, have been investigated in this study. Two kinds of imperfections, which are the initial ovality along cross -section direction and the winding-induced waves along longitudinal symmetric axis, are considered. Two numerical analyses including the non-linear finite element (FE) and elastic-plastic buckling analysis are performed by the commercial software MSC Marc/Mant 2005. The obtained results indicate that initial imperfections have an obvious influence on the collapse loads of both the Ti6Al4V-laminate composite submersible vessel and the Ti6Al4V one. The collapse load is mainly governed by the elastic-plastic buckling critical load, which is conservative and safe for a vessel to bear the admissible failure load under the deepwater. Moreover, the Ti6Al4V-laminate composite submersible vessel has a better capability to resist imperfections than the Ti6Al4V one.

Rolling horizon based multi‐objective robust voltage/VAR regulation with conservation voltage reduction in high PV‐penetrated distribution networks

Voltage/VAR regulation (VVR) implemented by capacitor banks (CBs), on-load tap changers (OLTCs), and photovoltaic (PV)-associated inverters is effective to enhance voltage stability and reduce power loss. On the other hand, conservation voltage reduction (CVR) has been widely adopted in distribution networks to reduce load demand. Existing works mainly focus on each of them. This paper proposes a VVR method with CVR, forming a multi-objective optimisation problem which minimises (i) voltage collapse proximity indicator (VCPI), (ii) load demand, and (iii) power loss. Besides, PV power generation as uncertainty significantly impairs the VVR results. To deal with the uncertainty issue, this paper proposes a rolling-horizon framework to determine VVR and applies Taguchi's orthogonal array testing (TOAT) to model the uncertain PV power generation, achieving rolling-horizon-based multi-objective robust VVR. The proposed model is tested and demonstrated on the IEEE 33-bus and 69-bus systems, and simulation results verify that the proposed method can support robust solutions of the multi-objective VVR problem for decision-making.

Application of the equivalent material concept to the study of the ductile failure due to U-notches

This paper studies the applicability of the Equivalent Material Concept to the fracture of elastoplastic materials due to the presence of U-notches. This approach consists of simplifying the study of an elastoplastic material by assuming linear elastic behaviour. The maximum stress of this fictitious material is such that the deformation energy in a tensile test would be the same as for the real material. This idea combined with a failure criterion allows to establish a procedure to predict the failure of U-notched elements. The methodology has been successfully applied to five elastoplastic materials. In all of them the ratio between the plasticity level at failure and the plastic collapse load has been determined. The proposed methodology has been carefully verified and application limits have been proposed when failure occurs within the small-scale yielding regime.

Numerical model and dynamic analysis of multi degree of freedom masonry arches

SummaryA new model is presented for planar multi‐block arches subjected to earthquakes. The blocks are assumed to be rigid, and every interface between the blocks may split open and may close, ie, the blocks may impact to each other. During impact, both the classical Housner's approach and improved models with lower energy dissipation are considered. The arch model is verified by comparisons with the available results in the literature. Using the new model, it was found that the circular arch moves as a four‐hinge mechanism typically only at the beginning of excitation, and several cracks split open during motion; furthermore, that modeling a multi‐block arch by a single degree of freedom (SDOF) four‐hinge mechanism may significantly overestimate its collapse load. While, in accordance with the literature, the overturning curves of single blocks and arches with symmetrically located four hinges are similar; for multi‐block arches where several hinges may occur they can be very different.

Collapse of honeycomb cell as a result of buckling or plastic hinges, analytical, numerical and experimental study

The honeycomb structure collapse during energy absorption and deformation is considered as one of the important subjects for researchers. In this paper, a combined analytical, numerical and experimental analysis on the collapse load of hexagonal aluminum honeycombs due to buckling or plastic collapse of the unit cells under flatwise compressive loading is performed. To analyze the collapse load, some analytical equations are derived for buckling and forming plastic hinges using the frame element. The amounts of these loads are measured for a single-row aluminum honeycomb structure, and the smallest one is selected as collapse load. The results show that the main cause of structure collapse is the formation of plastic hinges. To evaluate the analytical results and to propose a valid numerical simulation method, the quasi-static pressure test is performed. Furthermore, the structure collapse is also simulated by Abaqus software. The maximum difference between the numerical and experimental collapse load is 2.5%. Moreover, the deformed shape of the structure is very similar to the experimental one. The numerical simulation method and the proposed analytical relations can be used to analyze the collapse in other metal honeycomb structures.

Linear and non-linear analysis on two-dimensional steel frame under different temperatures

Purpose Progressive collapse because of high temperatures arising from an explosion, vehicle impact or fire is an important issue for structural failure in high-rise buildings. Design/methodology/approach The present study, using ABAQUS software for the analysis, investigated the progressive collapse of a two-dimensional, three-bay, four-storey steel frame structure from high-temperature stresses. Findings After structure reaches the temperature results like displacement, stress axial load and shear force are discussed. Research limitations/implications Different temperatures were applied to the columns at different heights of a structure framed with various materials. Progressive collapse load combinations were also applied as per general service administration guidelines. Originality/value This study covered both steady-state and transient-state conditions of a multistorey-frame building subjected to a rise in temperature in the corner columns and intermediate columns. The columns in the framed structure were subjected to high temperatures at different heights, and the resulting displacements, stresses and axial loads were obtained, analysed and discussed.

Linear analysis of a three-dimensional multistorey steel-frame structure under varying temperatures

PurposeThe purpose of this study is progressive collapse behavior in buildings. It occurs due to removal/damage of a column by fire, blast or vehicle impact.Design/methodology/approachThe present study investigates the comparative behavior of 3D four-storey moment resisting steel frame using ABAQUS to predict the sensitivity of the structure in progressive collapse because of fire loads. Columns at different levels were given different temperature with reduced material properties and yield strength. Progressive collapse load combination was adopted as per General Service Administration guidelines. Corner, middle, intermediate, multiple corner and multiple intermediate columns were subjected to fire load separately.FindingsThe results for displacement, stress, shear force and axial force were captured and discussed.Originality/valueThe study covers linear analysis of steel frame because of different temperature. In linear analysis. columns were subjected to different temperature and their results were studied. Effect of temperature in the structure were captured because of different fire conditions.

Seismic capacity and multi-mechanism analysis for dry-stack masonry arches subjected to hinge control

Masonry arches are vulnerable to seismic actions. Over the last few years, extensive research has been carried out to develop strategies and methods for their seismic assessment and strengthening. The application of constant horizontal accelerations to masonry arches is a well-known quasi-static method, which approximates dynamic loading effects and quantifies their stability, while tilting plane testing is a cheap and effective strategy for experimentation of arches made of dry-stack masonry. Also, the common strengthening techniques for masonry arches are mainly focusing on achieving full strength of the system rather than stability. Through experimentation of a dry-stack masonry arch it has been shown that the capacity of an arch can be increased, and the failure controlled by defining hinge positions through reinforcement. This paper utilizes experimentally obtained results to introduce: (1) static friction and resulting mechanisms; and (2) the post-minimum mechanism reinforcement requirements into the two-dimensional limit analysis-based kinematic collapse load calculator (KCLC) software designed for the static seismic analysis of dry-stack masonry arches. Computational results are validated against a series of experimental observations based on tilt plane tests and good agreement is obtained. Discrete element models to represent the masonry arch with different hinge configurations are also developed to establish a validation trifecta. The limiting mechanism to activate collapse of arches subjected to hinge control is investigated and insights into the optimal reinforcement to be installed in the arch are derived. It is envisaged that the current modelling approach can be used by engineers to understand stability under horizontal loads and develop strengthening criteria for masonry arches of their care.

Performance Assessment of RC Columns Subjected to Non-Uniform Fire Exposure

Fire in buildings is one of the most destructive accidental loads that may occur during its design lifetime which can significant loss of life and property. Past building fire incidents indicated the necessity of incorporation of its effect in structural design approaches. Currently, the fire design of RC columns is based on the prescriptive method suggested in National Building Code (NBC) 2016 and IS 456: 2000 which only provides minimum dimensions and cover values for various fire durations with an assumption that all column faces will be subjected to fire exposure simultaneously. However, in realistic scenarios the columns may be subjected to non-uniform/uniform fire scenarios viz. 1-, 2-, 3-face fire exposures are non-uniform and all 4 face fire exposures is uniform, depending on their location in building and location of fire. As the modern design approaches are moving towards the performance based design, the assumption of uniform fire case does not holds good. This paper presents a comparative study of column capacities subjected to non-uniform fire exposures computed using Tan and Yao method and compares with column capacities computed by zoning method of Eurocode-2. In this study a set of columns of an existing educational building with different fire exposure conditions are considered. The collapse load for those columns is determined by both Eurocode-2 method which considers uniform fire case and Tan and Yao method which considers non-uniform case. The variation in their collapse loads from both methods is shown. The study also provides the actual fire rating of columns subjected to non-uniform fires which is an aspect of public fire safety in buildings.

A Framework for Collapse Vulnerability Assessment of Steel Beams Subjected to Increasing Loads and Nonuniform Longitudinal Temperature

AbstractSteel beams are susceptible to large deformation and capacity reduction when subjected to elevated temperatures. Determination of collapse loads for structural steel members under fire is c...