General Purpose Finite Element Program Research Articles

Influence of elevated temperature on buckling capacity of mild steel-based cold-formed steel column sections– experimental investigation and finite element modelling

PurposeThe capability of steel columns to support their design loads is highly affected by the time of exposure and temperature magnitude, which causes deterioration of mechanical properties of steel under fire conditions. It is known that structural steel loses strength and stiffness as temperature increases, particularly above 400 °C. The duration of time in which steel is exposed to high temperatures also has an impact on how much strength it loses. The time-dependent response of steel is critical when estimating load carrying capacity of steel columns exposed to fire. Thus, investigating the structural response of cold-formed steel (CFS) columns is gaining more interest due to the nature of such structural elements.Design/methodology/approachIn this study, experiments were conducted on two CFS configurations: back-to-back (B-B) channel and toe-to-toe (T-T) channel sections. All CFS column specimens were exposed to different temperatures following the standard fire curve and cooled by air or water. A total of 14 tests were conducted to evaluate the capacity of the CFS sections. The axial resistance and yield deformation were noted for both section types at elevated temperatures. The CFS column sections were modelled to simulate the section's behaviour under various temperature exposures using the general-purpose finite element (FE) program ABAQUS. The results from FE modelling agreed well with the experimental results. Ultimate load of experiment and finite element model (FEM) are compared with each other. The difference in percentage and ratio between both are presented.FindingsThe results showed that B-B configuration showed better performance for all the investigated parameters than T-T sections. A noticeable loss in the ultimate strength of 34.5 and 65.6% was observed at 90 min (986℃) for B-B specimens cooled using air and water, respectively. However, the reduction was 29.9 and 46% in the T-T configuration, respectively.Originality/valueThis research paper focusses on assessing the buckling strength of heated CFS sections to analyse the mode of failure of CFS sections with B-B and T-T design configurations under the effect of elevated temperature.

Farklı açılardaki çeşitli çokgen delikli kare plakların burkulma analizi

Buckling of the plates is of great importance in design of structures. If the plate has a hole because of necessity, hole area and shape also affect the critical buckling loads. In this study, buckling analyses of perforated simply supported square plates with various perforation patterns and different loading types were investigated. Three different perforation patterns as circular, hexagonal and square with different orientations were considered. In order to investigate the slenderness ratio effect, samples were calculated with three different ratio values of 100, 20 and 10. The samples were loaded with four different in-plane loads to examine the effect of loading type. Analyses were performed by using a general purpose finite element program and critical buckling loads were determined depending on the orientation angles for square plate models with different hole perforations. The critical buckling load is independent from the orientation angle for circular perforated plates but depends on for hexagonal and square hole perforations. For these plates buckling analyses were performed for different orientation angles of 0 degrees to 90 degrees. The results show that the calculated critical buckling loads did not remain the same although the hole areas were the same.

A proposed approach for Pin-Fuse connections strengthened with pre-tensioned cables

A Pin-Fuse connection dissipates energy through a friction-slip mechanism during powerful earthquakes. Pin-Fuse connections are an innovative system that can be replaced after earthquakes and can sustain seismic energy with less harm to beams and columns. Herein, the monotonic response of the Pin-Fuse connection system strengthened by pre-tensioned cables is investigated. The strength, force–displacement diagram, and moment-rotation curve of the connection have been examined with various friction coefficients of 0, 0.6, and 0.9 together with various pre-tensioned cable forces. The general-purpose finite element program ABAQUS has been utilized to model the behavior of Pin-Fuse connections. The available test is used to validate the ABAQUS model. The result shows that in the systems with a friction effect, the presence of the pre-tensioned cables reduces the beam’s deflection and increases the tolerable bending moment of the system. The more the value of the pre-tensioned force, the more the system’s bearing capacity.

Predicting seismic damage on concrete gravity dams: a review

The seismic assessment of concrete gravity dams is a problem of prediction of cracking and the corresponding consequences. With the widespread use of general-purpose finite element programs, the work in the field has shifted towards quantifying the behaviour in a framework for assessment. The nonlinear analysis and coupling with foundation–reservoir interaction, conversely, is still a challenging task. The modelling approach has significant effects on the analysis results and the assessment framework. The field remains an active area for research with many outstanding issues regarding damage quantification and assessment compared to any other major infrastructure component. A comprehensive overview of the seismic assessment of gravity dams is presented in this work with the goal to outline the issues in the field. Different models and modelling choices are compared in the context of damaged state assessment of gravity dams. The links between practical difficulties and theoretical issues are critically discussed. The aleatoric and epistemic uncertainties in the field, and their sources, are presented. Areas of future work are identified for improvement in seismic assessment as well as reducing and quantifying the uncertainties in the prediction of damaged states for concrete gravity dams.

Efficient numerical analyses of RC beams subjected to impact loading using axial-flexure-shear fiber beam model

Similar to wind and seismic loading, impact loading induced by e.g. vessel or vehicle collisions is another type of extreme loading that has become one of the major hazards for the safety of our infrastructural systems such as bridges and buildings. The development of effective strategies which can realistically quantify structural responses under impact loading becomes increasingly important. The widely-used finite-element (FE) simulations using general-purpose FE programs often require excessively high computational cost. This paper therefore aims to develop and implement a computationally efficient axial-flexure-shear fiber beam model based on Timoshenko beam theory with consideration of material non-linearity for the analyses of reinforced concrete (RC) beams under impact loading. The axial, flexural and shear deformation of RC sections during impact are effectively coupled at the fiber and material level. Numerical accuracy of the proposed fiber beam model for non-linear dynamic impact analyses is verified using experimental data from 15 sets of drop-hammer impact tests on scaled RC beams, including flexure-dominant slender beams and shear-dominant deep beams, which demonstrate the great advantage of the proposed fiber beam model over the classical Euler–Bernoulli fiber beam model for applications to impact scenarios where shear deformation of RC members becomes non-negligible.

Shaking table test and numerical analysis of a coal-fired power plant equipped with large mass ratio multiple tuned mass damper (LMTMD)

In an industrial building, heavy equipment can be configured as the mass of multiple tuned mass dampers with large mass ratio (LMTMD) without the addition of extra mass. This paper systematically investigates the effects of the LMTMD for the mitigation of structural seismic responses in industrial buildings such as a coal-fired power plant. A detailed design method was proposed based on numerical modeling , optimization of the key parameters and evaluation of the seismic performance of the structure. Shaking table tests were conducted on a scaled model and time-history analysis were performed with general purpose finite element program ABAQUS. The coal-fired power plant with mass irregularity due to the installation of heavy coal buckets was selected as the sample structure. The heavy coal buckets are utilized as the mass of the LMTMD. The feasibility and effectiveness of the proposed design method were demonstrated through tests and analyses. The simulation results agree well with the test results, which validate the accuracy of the numerical analyses and suggest that the LMTMD can effectively reduce the structural dynamic response and significantly improve the seismic performance of the thermal power plant structure. The reduction rate of the maximum inter-story drift was more than 32.6% under earthquake excitations, demonstrating the effectiveness and strong robustness of the LMTMD. The failure mode of the structure was optimized by the reduced damage concentration. • A detailed design method for a structure equipped with LMTMD was proposed. • The feasibility and effectiveness of the design method were demonstrated through tests and numerical analyses. • Heavy coal buckets that cause the mass irregularity of the structure were utilized as the mass of the LMTMD. • The LMTMD can significantly improve the seismic performance of the thermal power plant structure.

Experimental and numerical investigation on torsion strength of light gauge SHS strengthened with CFRP wraps

In this research, an experimental and numerical investigation on the influence of strengthening steel square hollow sections (SHS) subjected to pure torsion with Carbon Fiber Reinforced Polymers (CFRP) wraps. CFRP was widely used to strengthen steel members in bending and compression. Experimental tests were conducted on 8 light-gauged steel SHS having two different cross-sections, SHS 48×2 mm, SHS 80×2 mm. Four strengthening configurations were tested; namely, Spiral, Reverse, Spiral-Reverse, and Reverse-Spiral. All specimens were wrapped with an orientation angle 45° with respect to the longitudinal axes of the specimen. Results showed that Spiral-Reverse and Reverse-Spiral configurations offered higher capacity enhancement. Strengthened specimens with these configurations reached up to 96% increase in their torsional capacity with respect to the control bare specimen. Spiral and Reverse configurations showed lower torsional capacity enhancement with a maximum percentage of 47%. Finite element models were constructed to simulate the tested specimens. The general purpose finite element program ANSYS was used to establish a numerical model for strengthened SHS incorporating geometric and material non-linearity. The numerical solution was essentially non-linear static analysis at which the load was applied incrementally using the arc-length method. The limit load of strengthened SHS was defined by the load at which the total strain energy reached 1.2 times that of respective bare SHS as per experimental results obtained herein. The proposed numerical model provided compatible results with test results obtained herein and previous literature.

Solving the Laplace Tidal Equations using Freely Available, Easily Extensible Finite Element Software

The Laplace Tidal Equations (LTEs) play a basic role for investigating the dissipation of long-term orbital energy as heat in surface oceans of icy satellites. Here we address solving LTEs by means of finite elements using PDE2D, a general-purpose finite element program for solving multidimensional PDEs. We use PDE2D to solve the equations for eccentricity and obliquity gravitational potentials for a shallow water approximation, and calculate ocean dissipation in three icy satellites, Enceladus, Europa and Titan. Compared with previous modeling procedures, PDE2D solves for unknowns that are approximated by piecewise cubic polynomials, thus attaining a higher O(dφ4) + O(dθ4) numerical precision. Our modeling results show, within few percent errors, a good agreement with earlier semi-analytical models and numerical solutions. We provide an open access to our PDE2D codes which are intended to be simple and easy to adjust for a wide range of tidal heating related problems. Our modeling results show that PDE2D can be a useful tool for researchers studying tidal heating related problems.

Effect of Slenderness Ratio on Fatigue Life of CFRP Strengthened Steel I-Beam

Carbon fiber reinforced polymers (CFRP) to repair and strengthen the steel I-beam has been increasingly used since last decade. CFRP composites bonded to steel members offer many advantages over steel plate bonding including excellent corrosion resistance, high stiffness and high strength to weight ratios etc. This study numerically investigates the fatigue performance of CFRP strengthened steel I-beam. One non-strengthened control beam and several strengthened beams using steel plates and CFRP strips were investigated primarily. The effect of slenderness ratios of web on fatigue behavior of CFRP strengthened steel I-beam is investigated. The beams were simulated in full three-dimension and fatigue life was investigated by using general-purpose finite element program, ANSYS. Simply supported beam subjected to two loads on compression flange is analyzed to show the effect of CFRP and slenderness ratios on fatigue behavior of steel I beam. The results show, that the life cycle of a CFRP strengthened beam before failure is higher than that of bare beam. It is also observed that beams with higher slenderness ratios (fixed thickness of the web) give better fatigue performance.

Crosspave: a multi-layer elastic analysis programme considering stress-dependent and cross-anisotropic behaviour of unbound aggregate pavement layers

ABSTRACT This manuscript describes the development of a new pavement analysis programme called CrossPave based on the Multi-Layered Elastic Theory (MLET) framework, but capable of accommodating stress-dependent and cross-anisotropic behaviour of unbound pavement layers. Generally, Finite Element (FE) based programmes such as ILLI-PAVE, MICH-PAVE, SENOL, GT-PAVE etc. or general-purpose FE programs with special user-defined material sub-routines have been used to model the stress-dependent nature of unbound materials. However, these FE programme are time consuming and need certain expertise, making them unfavourable for implementation into practice. Few MLET-based programmes such as KENLAYER and Everstress are capable of considering the stress-dependent nature of unbound materials, but fail to accommodate some of the recently developed material models. The newly developed pavement analysis programme, CrossPave, addresses these issues, and incorporates five different non-linear stress-dependent resilient modulus models for unbound materials. Details of the developmental effort are presented in this manuscript, along with results from validation efforts highlighting close agreement between KENLAYER, ILLI-PAVE and GT-PAVE. Critical pavement response parameters for two full-scale pavement sections were calculated using CrossPave, and have been compared against field-measured values. The CrossPave programme has been presented as an enhanced, ready-to-implement programme compared to other MLET-based alternatives.

A novel floor-isolated re-centering system for prefabricated modular mass timber construction – Concept development and preliminary evaluation

Prefabricated modular mass timber (MT) construction provides a resource-efficient, consistent-quality, and eco-friendly solution for the building industry. Connections that facilitate the assembly of prefabricated modules to form the final structure usually do not possess the characteristics needed for performance of these systems in high seismic zones. In this study, a novel seismic force resisting system called FIRMOCS that incorporates floor-isolation and re-centering techniques, is proposed for the prefabricated modular MT construction. Finite element models of the Floor Isolated Re-entering Modular Construction System (FIRMOCS) and of regular modular construction Seismic Force Resisting Systems (SFRS) were developed in ABAQUS, a general-purpose finite element program. The seismic performance of the regular prefabricated modular MT SFRS and that of FIRMOC systems was evaluated using nonlinear dynamic time-history analysis along the principles of the National Building Code of Canada. The preliminary results showed that FIRMOC Systems significantly reduced the seismic demand on the prefabricated modular MT construction, thus leading to improved seismic response. Using the proposed novel SFRS, an efficient and resilient prefabricated modular MT construction solutions can be achieved in high seismic zones.

TRIP Steels: A Multiscale Computational Simulation and Experimental Study of Heat Treatment and Mechanical Behavior.

A multiscale investigation of the microstructure and the mechanical behavior of TRIP steels is presented. A multi-phase field model is employed to predict the microstructure of a low-alloy TRIP700 steel during a two-stage heat treatment. The resulting stability of retained austenite is examined through the temperature. The phase field results are experimentally validated and implemented into a model for the kinetics of retained austenite during strain-induced transformation. The kinetics model is calibrated by using experimental data for the evolution of the martensite volume fraction in uniaxial tension. The transformation kinetics model is used together with homogenization methods for non-linear composites to develop a constitutive model for the mechanical behavior of the TRIP steel. A methodology for the numerical integration of the constitutive equations is developed and the model is implemented in a general-purpose finite element program (ABAQUS). Necking of a bar in uniaxial tension is simulated and “forming limit diagrams” (FLDs) for sheets made of TRIP steels are calculated. The models developed provide an integrated simulation toolkit for the computer-assisted design of TRIP steels and can be used to translate mechanical property requirements into optimised microstructural characteristics and to identify the appropriate processing routes.

Seismic Design Considerations for Architectural Design Aspects

Architectural design decisions play an important role in the earthquake behavior of buildings. However, architects are very unfamiliar with earthquake response concept. Earthquake resistant design (ERD) initiates generally during the architectural design stage to adhere to these principles. This study was focused on plan geometries, architectural design and structural system configurations for structural earthquake responses. A general-purpose finite element program was used to evaluate several irregularities and their corresponding earthquake responses. In the first phase of the study, the projections in plan view and projection ratios were compared from a torsional response perspective. In the second phase, nonparallel axes are investigated. In the last phase, the effects of shear wall arrangement on torsional irregularity response were analysed by considering 4 different configurations in a school building failure during the recent earthquake (2011) in the city, Van located in the east of Turkey. The number of storys was chosen as a parameter for the latter phase. The mode superposition method was preferred for the linear dynamic analyses. According to the results of the study, the torsional rotation was found to be proportional to the projection ratio in plan. For non-orthogonal cases, structure with an inclined axis more than 30°, torsional irregularity factor exceeded the code-defined limit. Beneficial observations and conclusions were drawn for both architects and structural engineers’ perspective.

Steel framed structures with cross laminated timber infill shear walls and semi-rigid connections

In recent years, hybrid steel-timber structures are seeing an increasing use in modern building construction at a competitive price. Cross-laminated timber (CLT) is a prefabricated multi-layer engineered panel wood product, manufactured by gluing layers of solid-sawn lumber at perpendicular angles. Their orientation results in excellent structural rigidity in both orthogonal directions. CLT construction materials are used not only for flooring systems and roof assemblies, but CLT infill shear walls are also gaining a lot of interest as a promising alternative for sustainable primary lateral load resistance systems. This paper extends the current research background on hybrid steel-timber structures. To achieve that, this work is conducted in such way as to explore the potentiality of incorporating CLT infill shear walls within steel framed structures with semi-rigid connections (STSW). In particular, a three-dimensional finite element model using the general-purpose finite ele-ment program ANSYS is generated herein to study the mechanical behaviour of a single-bay, two storey STSW system with semi-rigid connections. Analytical results show that the presence of CLT infill shear walls can significantly improve the performance of moment-resisting frame systems, for multi-storey buildings. Moreover, it is observed from the extended parametrical study that the STSW systems show better performance when an appropriate plastic moment ratio index is defined.

Calculation of coupled modes of fluid-structure systems by pseudo symmetric subspace iteration method

An efficient technique is proposed for calculation of coupled modes of fluid-structure interaction systems. The algorithm is presented with symmetric matrix operation mentality such that one feels that a symmetric eigen-problem is being solved. Furthermore, it is proved that each left eigen-vector is related to the corresponding right eigen-vector through a simple relation. Therefore, subsequent transient analysis can readily be performed. Overall, it is felt that the method is very efficient and it is ideal to be employed in general purpose finite element programs for solving above-mentioned eigen-problems

A strain-gradient isotropic elastoplastic damage model with J3 dependence

A “plastic-strain-gradient” version of an isotropic elastoplastic damage model that depends on the third invariant J3 of the stress deviator is developed. The model is based on the “non-local” equivalent plastic strain ep defined by Peerlings et al. (2001) and Engelen et al. (2003) and introduces a “material length” ℓ to the constitutive equations. It is shown that the non-local equivalent plastic strain ep at a material point P can be identified with the average value of the local von Mises equivalent plastic strain ε¯p over a sphere centered at P and of radius approximately equal to 3 ℓ. A methodology for the numerical integration of the constitutive equations is presented. The algorithm is appropriate for rate-independent as well as rate-dependent (viscoplastic) models. The model is implemented in the ABAQUS general-purpose finite element program and both quasi-static and dynamic problems are solved. Two possible ABAQUS implementations are discussed. First,“user elements” are developed, which can be used for the solution of both quasi-static and dynamic problems. Reduced 1-point Gauss integration is discussed in 8-node hexahedral elements and the “physical stabilization” method of Puso (2000) is used to remove the resulting numerical singularities (hourglass control). Second, the implementation of the model via “user material” subroutines is discussed. Quasi-static problems can be solved with ABAQUS/Standard using a *COUPLED TEMPERATURE-DISPLACEMENT, STEADY STATE analysis together with user subroutine UMAT, in which temperature is identified with the non-local equivalent plastic strain ep; the solution of dynamic problems requires use of ABAQUS/Explicit together with a *DYNAMIC TEMPERATURE-DISPLACEMENT analysis option and user subroutines VUMAT and DFLUX. Several example problems are solved.

General solution procedures to compute the stored energy density of conservative solids directly from experimental data

Energy-conservative, hyperelastic solids assume the existence of a stored energy density which relates stresses and strains for any deformation state. The usual approach to model such materials is to impose an analytical expression of the stored energy function as a function of some invariants and material parameters. These material parameters are best-fitted to available experimental data. This approach is good for analytical derivations but less optimal for data-driven computational approaches and for accurate and efficient finite element analyses. We show in this paper that the stored energy solution of a solid may be accurately obtained in a general case from suitable numerical procedures, regardless of the invariants being use, without using material parameters nor fitting any assumed analytical form. We explain two general, simple, computational procedures to solve the problem. The numerically computed stored energies may be used in general-purpose finite element programs, yielding more general procedures that have an efficiency equivalent to that of the classical approach, which uses pre-defined analytical “models” and fitting parameters.

Lateral-Torsional Buckling Behaviour of Triangularly Corrugated Web Beam

Lateral torsional buckling (LTB) is a common failure mode of large span beams. In this phenomenon, the beam becomes unstable along the unbraced length. This instability of beams can be identified by out-of-plane deflection and twisting. In this paper LTB strength of triangularly corrugated web beams under bending condition is investigated. Examined steel beams consist of two flanges and a thin triangularly corrugated web, connected by automatic welding. In the literature, the LTB strength problem of steel beams was dealt with mostly for steel beams with plate, sinusoidal and trapezoidal corrugated webs. Researches of the LTB behaviour of beams with triangularly corrugated webs were found out to be very limited. A parametric study is carried out for various beam spans and corrugation densities. A general-purpose finite element program (ABAQUS) was used. The corrugation densities adopted in this study represent practical geometries, which are common used for such structures in building practice. Plot showing the influence of compressed flange slenderness on value of reduction factor for LTB is presented. It is determined that existing buckling curves poorly describe the change of reduction factor depending on slenderness of compressed flange for triangularly corrugated web beams. Finally, recommendations were proposed for the design of simple supported steel beams with corrugated webs against lateral torsional buckling in accordance with numerical results.

Multiscale modeling of skeletal muscle tissues based on analytical and numerical homogenization

A novel multiscale modeling framework for skeletal muscles based on analytical and numerical homogenization methods is presented to study the mechanical muscle response at finite strains under three-dimensional loading conditions. First an analytical microstructure-based constitutive model is developed and numerically implemented in a general purpose finite element program. The analytical model takes into account explicitly the volume fractions, the material properties, and the spatial distribution of muscle's constituents by using homogenization techniques to bridge the different length scales of the muscle structure. Next, a numerical homogenization model is developed using periodic eroded Voronoi tessellation to virtually represent skeletal muscle microstructures. The eroded Voronoi unit cells are then resolved by finite element simulations and are used to assess the analytical homogenization model. The material parameters of the analytical model are identified successfully by use of available experimental data. The analytical model is found to be in very good agreement with the numerical model for the full range of loadings, and a wide range of different volume fractions and heterogeneity contrasts between muscle's constituents. A qualitative application of the model on fusiform and pennate muscle structures shows its efficiency to examine the effect of muscle fiber concentration variations in an organ-scale model simulation.

Analysis of Non-Uniform Shrinkage Effect in Box Girder Sections for Long-Span Continuous Rigid Frame Bridge

To consider the effect of non-uniform shrinkage of box girder sections on the long-term deformations of continuous rigid frame bridges, and to improve the prediction accuracy of analysis in the design phase, this paper proposes a new simulation technique for use with general-purpose finite element program. The non-uniform shrinkage effect of the box girder is transformed to an equivalent temperature gradient and then applied as external load onto the beam elements in the finite element analysis. Comparative analysis of the difference in deflections between uniform shrinkage and nonuniform shrinkage of the main girder was made for a vehicular bridge in reality using the proposed technique. The results indicate that the maximum deflection of box girder under the action of non-uniform shrinkage is much greater than that under the action of uniform shrinkage. The maximum downward deflection of the bridge girder caused by uniform shrinkage is 5.6 mm at 20 years after completion of bridge deck construction, whereas the maximum downward deflection caused by non-uniform shrinkage is 21.6 mm, which is 3.8 times larger. This study shows that the non-uniform shrinkage effect of the girder sections has a significant impact on the long-term deflection of continuous rigid frame bridge, and it can be accurately simulated by the proposed transformation technique.