Nonlinear Finite Element Analysis Model Research Articles

Study on the Effect of Burial Depth on Selection of Optimal Intensity Measures for Advanced Fragility Analysis of Horseshoe-Shaped Tunnels in Soft Soil

Seismic intensity measures (IMs) can directly affect the seismic risk assessment and the response characteristics of underground structures, especially when considering the key variable of burial depth. This means that the optimal seismic IMs must be selected to match the underground structure under different buried depth conditions. In the field of seismic engineering design, peak ground acceleration (PGA) is widely recognized as the optimal IM, especially in the seismic design code for aboveground structures. However, for the seismic evaluation of underground structures, the applicability and effectiveness still face certain doubts and discussions. In addition, the adverse effects of earthquakes on tunnels in soft soil are particularly prominent. This study aims to determine the optimal IMs applicable to different burial depths for horseshoe-shaped tunnels in soft soil using a nonlinear dynamic time history analysis method, and based on this, establish the seismic fragility curves that can accurately predict the probability of tunnel damage. The nonlinear finite element analysis model for the soil–tunnel interaction system was established. The effects of different burial depths on damage to horseshoe-shaped tunnels in soft soil were systematically studied. By adopting the incremental dynamic analysis (IDA) method and assessing the correlation, efficiency, practicality, and proficiency of the potential IMs, the optimal IMs were determined. The analysis indicates that PGA emerges as the optimal IM for shallow tunnels, whereas peak ground velocity (PGV) stands as the optimal IM for medium-depth tunnels. Furthermore, for deep tunnels, velocity spectral intensity (VSI) emerges as the optimal IM. Finally, the seismic fragility curves for horseshoe-shaped tunnels in soft soil were built. The proposed fragility curves can provide a quantitative tool for evaluating seismic disaster risk, and are of great significance for improving the overall seismic resistance and disaster resilience of society.

Seismic collapse performance assessment of high‐strength steel framed‐tube structures with shear links fabricated using low‐yield‐point steel

SummaryA high‐strength steel framed‐tube structure with shear links fabricated using low‐yield‐point steel (HSSFTS‐LYPSL) was developed in this study to improve the seismic performance and resilience of the conventional steel framed‐tube structure. When this HSSFTS‐LYPSL is subjected to strong earthquake excitation, its shear links undergo significant plastic deformation to dissipate seismic energy while critical components such as the spandrel beams and columns maintain their elasticity. Furthermore, the replacement of damaged links was facilitated by the use of bolted end‐plate connections. This study designed three typical HSSFTS‐LYPSL examples with 20, 30, and 40 stories to investigate the seismic collapse performances of HSSFTS‐LYPSLs at different seismic intensity levels. Three‐dimensional nonlinear finite element analysis models of these example structures were developed using the OpenSEES software, and the accuracy and effectiveness of the modeling approach was validated by comparing its results with those of quasi‐static tests on sub‐structure assemblies. Next, 40 records each of far‐field and pulse‐type near‐field ground motions were selected and applied with an incremental dynamic analysis (IDA) to obtain response curves for the example structures and calculate their collapse fragility curves and collapse margin ratios (CMRs) utilizing a modified collapse fragility model. Finally, based on the collapse fragility and seismic hazard curves, the seismic collapse risk probability curves of the HSSFTS‐LYPSLs were obtained under far‐ and near‐field earthquakes, revealing that at the maximum considered earthquake level, the CMR values ranged from 5.74 to 7.25 and from 4.85 to 6.67, respectively; at the very rare earthquake (VRE) level, the CMR values ranged from 3.83 to 4.85 and from 3.24 to 4.46, respectively. These results demonstrate that HSSFTS‐LYPSLs exhibit sufficient potential for seismic collapse resistance. As pulse‐type near‐field earthquakes had more significant and adverse impacts on the seismic collapse performances of the HSSFTS‐LYPSLs than far‐field earthquakes, the seismic collapse design of an HSSFTS‐LYPSL should particularly consider the influence of near‐field effects. In addition, the seismic hazard function had a greater effect on the structural seismic collapse risk curves than the collapse fragility function, suggesting that seismic collapse risk curves could provide a comprehensive assessment of HSSFTS‐LYPSL seismic collapse performance. Under far‐ and near‐field earthquakes, the annual collapse risk probabilities of the HSSFTS‐LYPSL examples at the VRE level were within 1.18 × 10−5–4.53 × 10−5, which is below the seismic collapse risk threshold recommended by others, indicating that HSSFTS‐LYPSLs can meet the fourth‐level performance objective of “no collapse failure at the VRE level.” However, this study only conducted seismic collapse and risk assessments using example HSSFTS‐LYPSLs; future research will focus on determining the seismic recovery capacities of and developing post‐earthquake repairability methodologies for HSSFTS‐LYPSLs.

Influence of overlay strength degradation on bond stresses of bridge deck system

This research paper intends to numerically investigate the impact of selected factors on the strength of the concrete overlay-bridge deck bond, directly and indirectly, using the nonlinear finite element analysis (NLFEA) method. Besides, the research introduces the guidelines necessary to attain adequate bond strength to eliminate the possibility of concrete detachment under the effect of different developed stresses. The NLFEA has been utilized in predicting and correlating the live applied loads and the induced shrinkage stresses at the interfacial region between the concrete overlay and the bridge deck. The developed stresses were related to the overlay's direct tensile bond strength. A total of 336 NLFEA models of overlay-bridge deck slab segments were designed and examined after being properly validated. The parameters of the study were as follows: the overlay degradation level (0 %, 19 %, 36 %, 51 %, 64 %, and 75 %); the ratio of the overlay's relative thickness-to-the bridge deck slab (toverlay/tslab); in addition to the age of the shrinkage induced stresses (early age (3 and 7 days) and moderate age (14 and 28 days)). The NLFEA live load and shrinkage stress values were validated using experimental results from the literature with difference percentages of less than 5 %. The numerical study results recommended that the thickness of the concrete's overlay should be within certain overlay thickness limits to be capable of handling the lower and higher stresses at the service and overloading conditions. The proposed guidelines enable the avoidance of unfavorable detachment between the interface parts under the effect of AASHTO HS-20 truck cyclic and impact loadings, as well as shrinkage loading.

NLFEA of the Behavior of Polypropylene-Fiber-Reinforced Concrete Slabs with Square Opening

The bending behavior of one-war reinforced concrete (RC) slabs with polypropylene fibers (PF) was examined in this study under the effect of different opening ratios using the nonlinear finite element analysis (NLFEA) method. The investigated parameters include the effect of different square opening ratios between 0 and 24% and PF volume percentages between 0 and 1% with 0.1% increments. The objectives of this study were fulfilled using 88 NLFEA models with different combinations of the studied parameters, including 11 control slabs without openings. The slab’s behavior was studied focusing on different structural performance characteristics, such as ductility, using energy-based and deflection-based approaches, stiffness (initial and yielding), cracking, and ultimate load strength. In addition, other structural performance parameters were considered, such as the crack opening, failure modes, and strain values, which were recorded for all specimens during the loading history. Moreover, the load-carrying capacity of the slabs was compared, looking at the NLFEA method’s results and the theoretical prediction results based on the sectional analysis method. However, it was observed that the inclusion of PFs of different percentages has a superior effect on the behavior of RC slabs with small openings (less than 2% opening ratio) compared to the acceptable improvements obtained for sabs with larger opening sizes. Consequently, PF could be utilized as a replacement for conventional steel rebars for RC slabs with small openings. In addition, increasing the PF percentage increases the resulting crack-opening value at failure due to the provided stabilization effect, in addition to increasing the system’s ability to sustain loads.

Treatment of lateral ankle joint ligament sprain by shaking and poking manipulation based on finite element method

To conduct a preliminary study on joint injuries of anterior and calcaneal fibular ligaments of the lateral ankle joint, and to analyze mechanism of action of shaking and poking in treating ankle joint and biomechanical properties of ankle during the recovery of joint injuries. CT scan was performed on a male volunteer with right ankle sprain. Mimics 10.0, Solidworks 2016, Hypermesh 12.0 and Abaqus 6.13 software were used to establish 3D nonlinear finite element analysis model of foot and ankle, and the validity of model was verified. Combined with clinical study, the finite element simulation analysis was carried out on the toe flexion, dorsiflexion, varus and valgus of ankle joint under different treatment periods by adjusting elastic modulus of ligament to simulate ligament injury. With the treatment of shake and prick and recovery of ligament injury, the maximum stress and area with large stress on tibial pitch and fibular joint surface gradually increased under the four working conditions, and the stress value of the maximum stress ligament gradually increased, and the stress of the anterior and calcaneal fibular ligament dispersed and transferred, and the axial force gradually decreased. The finite element method was used to simulate the mechanical condition of the shaking and stamping technique, and the changes of the forces of the ligament and articular surface before and after treatment of anterior and calcaneal ligament combined injury of ankle talus were intuitively observed. The treatment effect was quantified, and could provid objective and scientific basis for clinical promotion and application of this technique.

Full-scale testing and nonlinear finite element analysis of a pioneering fully prefabricated noise barrier wall system

The structural behavior of a novel fully prefabricated noise barrier wall system was examined experimentally and analytically using nonlinear finite element analysis. The wall components and connectivity details were developed to be a totally precast system for fast-track construction. Two full-scale prototypes were designed, fabricated, assembled, and prepared for full-scale testing at the High-Bay Structural Laboratory at the University of Illinois at Chicago. Each prototype was instrumented with about 40 sensors including strain gauges, linear variable differential transducers, and crack meters at pre-identified critical locations essential for understanding its structural behavior. In addition, a nonlinear finite element analysis model of the wall system prototype was required for future refinement and adjustment of the noise barrier wall system components. With proper calibration based on the experimental results, the nonlinear finite element analysis model will allow for conducting parametric studies on key factors relevant to the wall behavior without the need for costly and time-consuming full-scale testing. The structural behavior of the wall system was analyzed in terms of the load–deflection curves, load–strain curves, cracking, uplift, and failure mode. The experimental results revealed that the wall system was structurally stable up to a high loading level and met the intended serviceability and strength requirements.

Finite Element Investigation of Angle Ring Confinement for Clustered Large-size Stud Shear Connector in Full-Depth Precast Concrete Bridge Deck Panel

Full-Depth Precast Concrete (FDPC) bridge deck panel system, consisting of concrete deck and steel girders, has been used widely for highway and bridge construction due to rapid construction and replacement as well as in terms of economics. This system could integrate with clusters of large size headed-stud shear connectors for more significant connection, although larger composite actions were experienced. Therefore, a new angle steel ring confinement was introduced and tested by push-off samples for the most effective shear transfer. The Finite Element Analysis (FEA) of the push-off model with an in-depth investigation of non-linear concrete properties, boundary parameters, and different geometries of angle ring confinement was developed in this study. The FE models were verified with the push-off test in terms of loads, displacements, and failure stages. Nonlinear concrete material models: Concrete Damage (CD) and Drucker Prager (DP) were identified the different abilities either for predicting initial cracks, or determining maximum resistance and critical failure, respectively. The thickness of the angle and the sizes of hook bars were investigated for the most effective aspects of the angle ring confinement. The results showed comparable stiffness and load resistance for various aspects. However, compatible geometries, either 5 mm thick angles with DB12 hook bars or 10 mm angles with DB25 hook bars, were suggested. The final non-linear FEA model was reliable for comparative studies to FDPC push-off with different confinement configurations.

Tensile behaviors of stainless steel anchor channel systems embedded in concrete: Experimental and numerical analyses

Stainless steel anchor channels with channel bolts (SSAC-CBs) are extensively used in reinforced concrete structures subjected to corrosive environments owing to the excellent heat and corrosion resistance, appreciable inelastic deformation capacity, and high ductility of stainless steel. However, limited tests and numerical simulations have been conducted describing the tensile behaviors of SSAC-CB assemblies. We therefore conducted static monotonic tension tests to investigate the structural behaviors of SSAC-CBs embedded in concrete in terms of failure mode, tensile load-bearing capacity, ductility, and plastic development response. The test variables included the anchor/channel profile type, stainless steel grade, and tensile load position. The SSAC-CB specimens exhibited three dominant failure modes in tension: combined yielding of the channel lips and webs, flexural deformation of the channel, and concrete splitting. The ductility ratios of the test specimens ranged from 4.56 to 8.45, indicating a significant inelastic deformation capacity. Based on the maximum tensile loads obtained in the experiments, the ultimate limit state principle was employed to recommend tensile design resistances according to anchor channel type. In addition, nonlinear finite element analysis models were constructed in ABAQUS using three-dimensional solid elements to facilitate detailed investigations of the tensile behaviors of SSAC-CBs embedded in concrete; the numerically obtained failure modes and loads agreed well with the experimental responses. Finally, the experimental data were applied to propose and validate analytical expressions for the tensile load-bearing capacities of SSAC-CBs embedded in concrete corresponding to their different failure modes under tensile load.

Axial load-carrying capacity of concrete-filled steel tube columns: a comparative analysis of various modeling techniques

Limited research is available in the literature to investigate the presentation of normal strength concrete-filled steel tube (CFST) circular compression elements under compression loading by considering various material and geometric coefficients. Thus, the present study investigates the mechanical behavior of CFST compression elements employing nonlinear finite element analysis (NLFEA), empirical/theoretical modeling, and a newly developed Artificial Neural Network (ANN) model, based on a large experimental database of 1223 samples. The NLFEA modeling is performed in ABAQUS (6.14) with an improved concrete damaged plasticity model for laterally restrained concrete. Various geometric and material properties are considered, for parametric NLFEA estimates preliminary validated toward the available experimental database. A new ANN model for the load-carrying capacity of CFST circular elements was also offered by employing the experimental database. The comparison between the calculations of the NLFEA model, empirical model, and ANN model displayed a close agreement with the database results.

Predicting the behavior of RC T-beams strengthened with NSMCFRP rods in the negative moment region: a finite element approach for low cyclic loading

In this study, a finite element (FE) model for nonlinear FE analysis was developed to evaluate the performance of reinforced concrete (RC) T-beams, which were strengthened in the negative moment region by near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods under low cyclic loading. Furthermore, the rods' depth of embedment was the research variable. Every component of the beam is considered in the model, including the concrete, steel rebars, CFRP rod, CFRP sheet, adhesive, and stirrups. The nonlinear properties of concrete, steel rebars, and adhesive were taken into account, while that of the CFRP was assumed to be linearly elastic till rupture. In addition, the user-programmable capabilities of ABAQUS were used to define the degradation of each material under low cyclic loading. The developed FE model was then compared to some experimental measurements comprising two specimens strengthened with NSM-CFRP rods and one un-strengthened control specimen. Overall, the predicted FE mid-span deflection responses were in line with the corresponding measured experimentally tested data. Finally, the research findings were summarized.

Rate-dependent constitutive model of high-strength reinforcing steel HTRB600E in tension

High-strength reinforcing steel HTRB600E has significant potential application in reinforced concrete (RC) structures because of its high strength and ductility. Under the risk that structures with HTRB600E are subjected to severe dynamic loadings, the rate-dependent behavior and constitutive model of HTRB600E need to be investigated to provide a basis for the structural analysis. A series of tension tests were carried out to acquire the engineering stress–strain curves of HTRB600E in the strain rate range from 0.00025 to 590 s−1. Moreover, a hybrid experimental–numerical converse method was used to obtain the true stress–strain curves beyond the necking of HTRB600E at different strain rates. The test results indicate that the strain rate significantly affects the mechanical properties of HTRB600E. The effect of strain rate on yield and ultimate tensile strength, uniform elongation, and yield to tensile ratio of HTRB600E was discussed. Three commonly-used models were calibrated or modified to predict the dynamic increase factors (DIFs) for yield and ultimate tensile strength of HTRB600E. A rate-dependent constitutive model for the engineering stress–strain curves modified from the Mander model was presented for the structure's analytical model based on the section analysis technique. A new rate-dependent constitutive model for the true stress-plastic strain relationship with necking behavior was proposed for the structure's nonlinear finite element analysis model. The formulations of DIFs and constitutive models agree with the test results well.

Effect of the Location of Broken Wires on Prestressed Concrete Cylinder Pipes under Working Pressure

The precise analysis of the overall mechanical performance of prestressed concrete cylinder pipes (PCCPs) with broken wires is a complicated problem. In this article, powerful finite element numerical means are applied to solve this problem. Firstly, the advantages and shortcomings of the current prestress simulation methods in the finite element analysis (FEA) literature are discussed, and the initial stress method based on a novel single-spring joint element method to model the pre-stress of wires is proposed. Then, different distributions of broken zones, including random broken distributions, are developed for two typical PCCP pipes with different wire-wrapped layers. The established nonlinear FEA model considers actual service processes such as manufacturing, installation and operation to investigate the mechanical behavior of two typical PCCP pipes with different breakage distribution regions and breakage ratios, and in particular, the overall mechanical behavior of a pipe with random breakage is determined first. To verify the accuracy of the proposed pre-stress simulation method and the established nonlinear finite element model, the overall mechanical response of a pipe before wires broke is compared with the results obtained via the specifications. The computed results under the corresponding breakage assumptions are consistent with the conclusions in the existing literature, providing important guidance for pipeline management and operation.

Impact of elevated temperature on the behavior of full-scale concrete bridge deck slabs reinforced with GFRP bars

The fiber reinforced polymer (FRP)-concrete composite bridge deck is expected to be a competitive alternative to the reinforced concrete bridge deck owing to its great durability, low weight, and high loading efficacy. The advantages of glass fiber reinforced polymer (GFRP) reinforcement in relation to heated damaged full-scale concrete bridge deck slabs encourage the extension of knowledge regarding the possibilities of combining the GFRP and heated damaged concrete to use the synergy of benefits that can be achieved in the construction and/or rehabilitation of bridges. This study presents a three-dimensional nonlinear finite element analysis (NLFEA) simulating the response of full-scale concrete bridge deck slabs reinforced with GFRP bars. A control slab model was developed initially and properly calibrated and validated against published independent experimental results. A parametric study was then conducted through creating twenty-four NLFEA models with different parameters: type of reinforcement (GFRP and steel), bottom transverse reinforcement ratio (ρ of 0.38, 0.46, and 0.57), and elevated temperature (20 °C, 100 °C, 200 °C, and 300 °C). The GFRP bars reinforcement of bridge deck slabs had superior effects on the ultimate load, elastic stiffness, post cracking stiffness, elastic energy absorption and post cracking energy and a little impact on ultimate deflection compared with steel reinforcement and the efficiency of GFRP bars increased with the heated damage level. Punching shear failure with a very similar cracking pattern was observed almost in all slabs and the bottom transverse reinforcement ratio is the main parameter affecting the tensile strains.

Seismic performance of two-story subway station structures with different isolating systems

When the sliding bearing is fixed only at the top of the middle column of the underground structure, the cracks at the side end of the middle plate should be aggravated while the seismic damage of the mid-column should be alleviated. To enhance the seismic performance of the mid-plate, a new isolation design method has been mentioned while the elastic sliding bearings are set at the top of the mid-columns and between the side end of the mid-plate and the side wall at the same time. By establishing a nonlinear finite element analysis model for the static-dynamic coupling interaction system, the seismic response characteristics of the cast-in-place station structure without a sliding bearing have been analyzed and compared with those of the station structure with the sliding bearing fixed only at the top of the middle columns, and those of the station structure with sliding bearing be fixed between the mid-plate and the sidewall at the same time. The results show that the new isolation station structures suffer fewer earthquake damages at the mid-plate and mid-columns at the same time, which can improve the overall seismic performance of the subway station structure.

Nonlinear vibration modeling and analysis of bolted thin plate based on non-uniformly distributed complex spring elements

Due to the existence of bolt influence zone, the interface pressure of bolted joint presents a non-uniform distribution. The nonlinear mechanical behaviors of variable stiffness and variable damping will also occur in bolted joints under varying degrees of forced vibration. In this paper, a nonlinear finite element analysis model of bolted thin plate is established by introducing displacement-dependent nonlinear complex spring elements with non-uniformly distributed parameters. Sinusoidal, parabolic and linearly distributed complex spring elements are used to simulate the non-uniform pressure distribution in the bolt influence zone, respectively. The stiffness and damping displacement-dependent parameters of the complex spring elements are described by higher-order polynomials, and a method to obtain the above parameters by inverse identification is proposed. In the case study, the non-linear finite element model created is used to calculate the resonance frequency and frequency domain response of bolted thin plate under five excitation levels. The maximum differences between the results and the measured values are 2.7% and 0.66%, respectively. The simulation results also reproduce the soft nonlinear vibration phenomenon of the bolted thin plate. Furthermore, by comparing the vibration analysis results of the linear model and nonlinear model for bolted thin plate, the reason for the soft nonlinear phenomenon produced is explained.

Effect of number of implants, distal implant inclination, and angled abutment on stresses in fixed complete dentures: a nonlinear finite element analysis

Objectives: This nonlinear three-dimensional finite element analysis (FEA) study evaluated the effect of the number of implants, distal implant inclination, and use of angled abutments on stress magnitude and distribution in cortical bone (CB), abutment screw (AS), and prosthetic screw (PS) of implant-supported fixed complete dentures. Methods: Nonlinear 3D FEA models of mandibular fixed complete dentures were created with five, four, or three parallel straight implants (5S, 4S, 3S) and with tilted distal implants (5T, 4T, 3T). In addition, the 5T model was tested using angled abutments over the tilted distal implants to re-align the implant inclination. A 100-N axial load was applied over the first molar region (cantilever) to analyze the von Mises stresses in selected points (CB, AS, and PS). Results: The implant adjacent to the load showed the highest stresses in CB, AS, and PS. The model with three implants showed higher stresses than the ones with four and five implants. Peak stresses in the AS increased 40% from five to four implants and 100% from five to three implants. Tilting the distal implants increased stresses in CB. Peak stress in the PS increased 150% from 5S to 5T models and 100% from 4S to 4T models. Angled abutments generated lower stresses on CB and AS but higher stresses on PS. Conclusions: The results suggest that stresses in the cortical bone, abutment screw, and prosthetic screw increase when tilting the posterior implants and reducing the number of implants. The use of angled abutments decreased stresses at the bone-implant interface and in abutment screws but increased stresses on prosthetic screws.

The biomechanical influence of facet joint parameters on corresponding segment in the lumbar spine: a new visualization method

Facet joints have been discussed as influential factors in the development of lumbar degeneration, which includes disc herniation and degenerative lumbar spondylolisthesis. Facet orientation (FO) and facet tropism (FT) are two important structural parameters of the lumbar facet joints. Many previous studies have focused on single parameter analysis of the lumbar spine. Owing to the correlation between independent variables, single-factor analysis cannot reflect the interaction between variables; however, there has been no corresponding biomechanical method developed to address this problem. To investigate the complex biomechanical influences on the lumbar spine when vertebral FO and FT are varied using finite element analysis (FEA) and contour maps visualization, and analyze the biomechanical role of facet joint structural parameters in the process of lumbar degenerative diseases. A biomechanical modelling, analysis, and verification study was performed. A three-dimensional non-linear FEA model of 3 denucleated intervertebral discs (L2-3, L3-4, L4-5) with adjacent vertebral bodies (L2-L5) was created. Previously performed in vitro experiments provided experimental data for the range of motion in each load direction that was used for calibration. For 12 lumbar models, different facet joint angles relative to the sagittal plane at both L3-4 facet joints were simulated for 35°≤FO≤50° and 0°≤FT≤15°. By modifying different values of FO and FT, FEA simulation of different lumbar spine models was performed. Contour maps were used to visualize the FO- and FT-relevant data. Under flexion, extension, and torsion moments, facet joint contact force and intradiscal stress increased with increasing FT. In the condition where FT remained 0° and increasing FO values, facet joint contact force and intradiscal stress remained low with no apparent increasing or decreasing trend when the model was under flexion, extension, and torsion moments. In the condition where FO and the FT values were varied at the same time, the highest force and stress regions in the contour maps were observed when all three types of moments were applied. Stress distributions of the L3-4 disc with different FT and FO values showed disc stress increased significantly with increases of FT and was concentrated on the ipsilateral region of the facet joint with the more sagittal orientation. The combination of FO and FT has an important impact on the corresponding disc and facet joints, but FT played a more significant role. Moreover, disc stress was concentrated on the ipsilateral region of facet joint with greater sagittal orientation when FT existed. FT with high sagittal orientation may increase risk of recurrent LDH due to increase ipsilateral disc pressure. These biomechanical findings may help clinicians to understand the prognosis of some lumbar degenerative conditions.

Finite element analysis of 90 degree pipe elbow sustained stress indices

Paper deals in-depth with the topic of sustained stress indices applicable to 90° elbows based on non-linear finite element analysis models. A comprehensive overview of the existing literature sources is given in the first part of the paper, showing that there are little sources which deal specifically with this topic and that the ones that do exist result in important scatter of the results. As a result, more than few of the existing sources are non-conservative in their nature. Dedicated non-linear finite element studies have been performed on shell and solid models which are used in conjunction with the regression analysis in order to obtain explicit equations which can be used to calculate both in- and out-plane sustained stress indices in 90° pipe elbows, which can then be used in the typical pipe stress analysis. Newly proposed equations prove to be a good fit for the numerical data, showing little deviation as shown by the correlation parameters presented in the paper. Final part of the paper presents a dedicated section on the high wall thickness elbows and shows the relationship between elbow wall thickness and maximum stress location. It is shown that beyond certain thickness, the maximum stress location shifts from the typical failure location (i.e., side wall) to the locations which are not typically expected (i.e., intrados or even away from elbow). This shifting may have an important effect on the theoretical models which assume failure location.

Response of interior beam-column connections integrated with various schemes of CFRP composites

This study evaluates the effectiveness of integrating Carbon Fiber Reinforced Polymer (CFRP) composites for improving the response of interior Beam-Column (B-C) connections under the combined effects of axial and lateral cyclic loads. Eighteen Reinforced Concrete (RC) B-C connection models were simulated using the nonlinear Finite Element Analysis (FEA) ANSYS software. The beam had a cross-sectional dimensions of 125 × 160 mm with a total length of 1600 mm, and the column cross-sectional dimensions were 125 × 150 mm with a total height of 1050 mm. Different parameters were taken into consideration in this study including: the configuration, orientation, length, and number of layers of CFRP sheets. The nonlinear FEA models were calibrated and reasonably validated based on experimental test results previously published in reputable journals. The response of the B-C connections was then evaluated in terms of mode of failure, stress contours, hysteretic loops, load-displacement envelopes, ultimate lateral load and corresponding drift displacement, and energy dissipation. The nonlinear FEA results showed that the used strengthening schemes of CFRP composites can significantly enhance the B-C connection performance leading to higher lateral load and drift capacities as well as energy dissipation. The effectiveness of the employed CFRP composite increased as the bonding area and number of CFRP sheet layers increased. The orientation angle of the CFRP sheets had had a considerable effect on the energy dissipation and minor effect on the ultimate lateral load and corresponding drift.

Strength of eccentrically loaded slender columns made with high-strength concrete

A non-linear finite-element analysis model was developed to predict the strength of high-strength concrete (HSC) slender columns. The studied parameters were compressive strength, load eccentricity, slenderness ratio and longitudinal and transverse reinforcement ratio. The model results were verified by comparison with analytical results and experimental results reported in the literature. A parametric study was also carried out by comparing the model results with those obtained using design codes, which were predominantly based on data derived from tests on normal-strength concrete. The model proved to be a suitable tool for the strength analysis of slender HSC columns. ACI 318-14 gave the most conservative predictions of the load-carrying capacity of centrally loaded columns but was close to the model results for eccentric loading. The procedures specified by BS EN 1992-1-1:2004 resulted in a significant underestimation of the load-carrying capacity of slender columns, particularly for eccentric loading, and this increased with greater slenderness ratios. This is probably because the confinement index taken into consideration in the software was not consistent, ranging from 0·03% to 5·14%. It was concluded that special clauses need to be introduced in the design codes for the accurate design of HSC columns.