Ultimate Moment Research Articles

Experimental study and finite element modelling of the torsional behavior of self-compacting reinforced concrete (SCRC) beams strengthened by GFRP

The present study experimentally and numerically investigates the behavior of ten self-compacting reinforced concrete (SCRC) beams strengthened by various means of externally bonded glass fiber reinforced polymer (GFRP) strips and subjected to pure torsion. The experimental matrix is designed to explore the impact of the number of GFRP layers, the width of the strengthening layers, and the spacing between those layers on the ultimate torsional capacity, the ultimate angle of twist, ductility, and failure patterns with respect to an un-strengthened specimen. Tests revealed that the specimen that was strengthened along its whole length using three layers of GFRP sheets yielded the highest gain in the ultimate torsional moment of 33.3% compared to the un-strengthened specimen. Additionally, the highest gain in the energy dissipation capacity among all strengthened beams (209.4% higher than the control beam) was obtained when four layers of GFRP sheets spaced every 300 mm were installed. Moreover, a three-dimensional (3D) non-linear finite element analysis is carried out via ABAQUS software to predict the torsional characteristics of SCRC beams either strengthened by GFRP strips or kept bare. The numerical model well captured the failure patterns, torque versus angle of twist responses, stress distribution, and the ultimate load of SCRC beams strengthened by GFRP strips with respect to the experimental findings.

The feasibility of using ultra-high performance concrete (UHPC) to strengthen RC beams in torsion

To explore the feasibility of using ultra-high performance concrete (UHPC) to strengthen reinforced concrete (RC) beams in torsion, pure torsion tests on 9 specimens have been conducted in this study, including one RC beam without strengthening (referred as control beam) and 8 UHPC-strengthened beams. The variables considered for investigation included the wrapping form of UHPC layer, thickness of UHPC layer, shape of steel fibers added in UHPC layer, UHPC-RC interfacial treatment, and reinforcement ratio of UHPC layer. The overall torsional behavior, torque–twist curves, torque-principal strain curves, cracking pattern and UHPC-RC interfacial slippage for all specimens were obtained based on the torsion tests. Results show that the cracking and ultimate torsional moments of all strengthened beams were higher than those of the control beam, with maximum increases of 488.5% and 593.2%, respectively. When the RC beam cannot be fully wrapped, which is the preferred strengthening scheme, 3-sided wrapping form is also an acceptable choice, but the 2-sided strengthening scheme should be avoided. The determination of the thickness of UHPC layer should comprehensively consider the strengthening effect, cost for strengthening and requirements for RC beam's dimensions after strengthening. RC beam surfaces should be fully roughened before casting UHPC to ensure that the UHPC layers and the RC beam persistently act together as a whole to resist torsional loads. The UHPC layers are recommended to be equipped with steel bars, which could substantially improve the torsional capacity and ductility of the strengthened beam on the premise of limited increase in the cost. Finally, the effectiveness of torsional strengthening using UHPC was compared with that using fiber reinforced polymer (FRP) in terms of increase in cross-sectional area, increases in cracking and ultimate torsional moments, increase in torsional stiffness, failure mode and long-term performance.

Structural assessment of the stalled building in Department of Industrial Engineering, Andalas University, Indonesia

The construction of the Industrial Engineering Department building is an effort to support the educational infrastructure at Andalas University. However, the building construction process was stopped because the contractor had terminated the contract (breach of contract) and it took a long time to continue the construction. Before that, a structural evaluation of the building structure should be conducted due to the update of the building standards. In this study, the structural evaluation was carried out by analyzing and modelling the building using ETABS v.18 software, as well as loading analysis on the building regarding current Indonesian building standards such as SNI 1726-2019 for earthquake resistance building design, SNI 2847-2019 for requirements of the structural concrete building and SNI 1727-2020 for building minimum design loads. The results of the analysis show that several structural beams did not have a strong enough capacity to withstand the working loads, where the ultimate moment and shear values due to the influence of acting loads were more than the nominal moments and shear values. Retrofitting of the weak structural beams using the CFRP wrapping method was recommended to improve the structural capacity of the building.

Longitudinal alterations in bone morphometry, mechanical integrity and composition in Type-2 diabetes in a Zucker diabetic fatty (ZDF) rat.

Individuals with Type-2 Diabetes (T2D) have an increased risk of bone fracture, without a reduction in bone mineral density. It is hypothesised that the hyperglycaemic state caused by T2D forms an excess of Advanced Glycated End-products (AGEs) in the organic matrix of bone, which are thought to stiffen the collagen network and lead to impaired mechanical properties. However, the mechanisms are not well understood. This study aimed to investigate the geometrical, structural and material properties of diabetic cortical bone during the development and progression of T2D in ZDF (fa/fa) rats at 12-, 26- and 46-weeks of age. Longitudinal bone growth was impaired as early as 12-weeks of age and by 46-weeks bone size was significantly reduced in ZDF (fa/fa) rats versus controls (fa/+). Diabetic rats had significant structural deficits, such as bending rigidity, ultimate moment and energy-to-failure measured via three-point bend testing. Tissue material properties, measured by taking bone geometry into account, were altered as the disease progressed, with significant reductions in yield and ultimate strength for ZDF (fa/fa) rats at 46-weeks. FTIR analysis on cortical bone powder demonstrated that the tissue material deficits coincided with changes in tissue composition, in ZDF (fa/fa) rats with long-term diabetes having a reduced carbonate:phosphate ratio and increased acid phosphate content when compared to age-matched controls, indicative of an altered bone turnover process. AGE accumulation, measured via fluorescent assays, was higher in the skin of ZDF (fa/fa) rats with long-term T2D, bone AGEs did not differ between strains and neither AGEs correlated with bone strength. In conclusion, bone fragility in the diabetic ZDF (fa/fa) rats likely occurs through a multifactorial mechanism influenced initially by impaired bone growth and development and proceeding to an altered bone turnover process that reduces bone quality and impairs biomechanical properties as the disease progresses.

Numerical Assessment on Continuous Reinforced Normal-Strength Concrete and High-Strength Concrete Beams

High-strength concrete (HSC) has been broadly applied to various civil structures for its advantages including high compressive strength and excellent durability and creep resistance. However, the brittleness of HSC raises concern about its use in practice. So far study on continuous reinforced HSC beams is limited. This work investigates the structural response of reinforced HSC continuous beams, and the results are compared with those of the counterparts made of normal-strength concrete (NSC). By applying a finite element method verified by experimental data, a comprehensive assessment is performed on two-span reinforced NSC and HSC (compressive strengths of 30, 60 and 90 MPa) continuous beams. A wide range of flexural reinforcement ratios are used to cover both under-reinforced and over-reinforced beams. The results show that reinforced HSC beams exhibit better flexural performance in terms of ultimate load, deformation, flexural ductility and moment redistribution, when compared to reinforced NSC beams. Formulae relating flexural ductility and moment redistribution with either neutral axis depth or tensile steel strain are suggested.

Experimental Study on the Flexural Behavior of Connected Precast Concrete Square Piles

Part of deep foundation pit support engineering needs to select connected precast concrete square piles (CPCSPs). Under the premise that the quality of precast concrete square piles (PCSPs) meets engineering requirements, the quality of CPCSPs becomes the key factor to ensure the safety of foundation pit support structures. This paper puts forward a new connection technology of CPCSPs and carries out the flexural behavior experiment of unconnected precast concrete square piles (UPCSPs) and CPCSPs. The distribution of crack and strain on different surfaces of UPCSPs and CPCSPs are measured by carbon fiber composite strain sense optical cables, glass fiber composite strain sense optical cables, and fixed-point polyurethane strain sense optical cables. The anti-crack load, ultimate load, bending moment, and flexural deformation of UPCSPs and CPCSPs are measured. The experimental results of UPCSPs and CPCSPs are compared. The results show that the anti-crack strength of CPCSPs is greatly increased while the flexural deformation of CPCSPs is decreased before the occurrence of crack. With the development of crack (failure stage), the outside areas of hoop steel plate exhibit cracks. At this moment, the strength of CPCSPs is no longer controlled by the strength of middle areas. The ultimate strength of CPCSPs is basically equivalent to that of UPCSPs. The ultimate bending moment of CPCSPs is higher than its design value (about 66%∼76%). The selection of CPCSPs in the design of foundation pit support has good reliability.

Numerical investigation and design of P-M interaction capacity of CFRP-jacketed hexagonal CFST short beam-columns

Hexagonal Concrete-Filled Steel Tubular (H-CFST) members are now widely recognized by engineers. A serious concern with these columns is the local buckling of thin-walled steel tubes, which Carbon Fiber-Reinforced Polymer (CFRP) sheets offer considerable help in eliminating this troublesome condition. The objective of this study is to evaluate the structural performance of short H-CFST columns stiffened by CFRP strips through nonlinear analysis and numerical simulation. First, the finite element (FE) models were validated against the previous test results, and a close agreement was achieved. Next, an organized parametric study was carried out to investigate the influence of a collection of vital parameters on the strength of the columns. The ultimate eccentric loads of the columns were computed, and the results were plotted as load-moment (P-M) interaction diagrams. The confining contact stress methodology between the steel tube and the concrete infill was in depth discussed, and it was found that the stress concentration is greater in CFRP-jacketed H-CFST columns than in bare ones, and its value is greatest in the corners. Based on the parametric study within the considered geometric and material ranges, using CFRP sheets effectively improves the confinement effect of steel tubes to the core concrete and enhances the strength of the columns by up to 35%. However, by using fully-wrapped CFRP layers, the columns could handle a maximum of 55% more load-carrying capacity. Finally, a modified design formula based on a unified theory was suggested to estimate the ultimate load and bending moment capacity of H-CFST short columns under eccentric loading.

EVALUASI KAPASITAS STRUKTUR EKSISTING LANTAI JEMBATAN PADA JEMBATAN TYPE PILE SLAB DI RUAS JALAN TOL JORR W1 KEBON JERUK

This research a study transverse cracking that occurred on the floor structure of the pile slab type bridge located at JORR W1 Kebon Jeruk toll road. The purpose of this study was to evaluate the capacity of the bridge floor structure that had damaged by cracks and weather its remains are in a safe condition or not. The research method is carried out by analyzing the calculation of loading that occurred in an actual condition that had cracked by modeling on structural analysis program with standard SNI 1725:2016 and actual loads that acted on the structure, then evaluating the moment capacity of the structure based on installed reinforcement and evaluating deflection from inspection results based permissible deflection. From the results of the analysis, it was found that the structure experienced a moment failure due to the actual load with a load magnitude of 18,07 tons, the moment due to the actual load on the negative moment region was 34,47 tons.m and the positive moment region was 37,46 tons.m, compared to the moment capacity of structure successively which was 25,52 tons.m and 29,16 tons.m. However, for the results of the analysis of the standard load of 11,25 tons, the moment capacity of the structure was able to withstand the ultimate moment due to the reactor load successively being 22,82 tons.m and 24,37 tons.m, whereas for the deflection test results of 0,46 mm remained in a safe condition without exceeding the L/800 permit deflection of 4,76 mm. Based on the results of the analysis, it can be concluded that the structure is overloaded and in the future, the structural ability must be improved and it is necessary to strengthen the bridge floor structure to be able to increase the capacity of the structure so that it can withstand the working load.

Experimental and numerical study of the flexural response of Ultra High Performance Concrete (UHPC) beams reinforced with GFRP

This paper investigates the flexural behavior of Ultra High Performance Concrete (UHPC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. A series of four-point loadings tests were conducted on full-scale beams reinforced with Glass FRP (GFRP) bars. The GFRP-UHPC beams were designed as either under-reinforced or over-reinforced to examine the differences in their failure modes. Steel reinforced beams, serving as reference specimens, were also cast and tested. All the beams measured 185 mm in width, 250 mm in depth, and 2200 mm in length. The influence of reinforcement ratio, number of bars, and surface texture of GFRP bars on the flexural behavior was studied. The test results showed that changing the mode of failure from GFRP rupture to concrete crushing improved the ductility flexural capacity of the UHPC beams. It was also shown that the bending stiffnesses, flexural capacities, and strain responses of the UHPC beams were enhanced upon increasing the reinforcement ratio. The experimental data was compared with the ACI 440 and CAN/CSA S806 code provisions. It was found that the recent ACI440 ultimate moment equation provided acceptable results for the under-reinforced beams but was slightly unconservative for the over-reinforced beams. A nonlinear finite element (FE) model was also developed considering both material and geometric nonlinearities using ABAQUS. The developed FE model verified well with the experimental results and can be utilized to simulate different loading scenarios and sections of GFRP UHPC beams.

An artificial neural network for predicting the ultimate bending moments in reinforced concrete beams with fiber-reinforced polymer strengthening

An artificial neural network for predicting the ultimate bending moments in reinforced concrete beams with fiber-reinforced polymer strengthening

Bending Deformation and Ultimate Moment Calculation of Screen Pipes in Offshore Sand Control Completion

Horizontal wells, extended-reach wells, and multi-branch wells were often used to exploit subsea oil and gas efficiently. However, during the sand control screen completion of those wells, the sand control screen pipe was easily deformed. Failure occurred when passing through the bending section due to the large bending section in the wellbore trajectory. A parametric analysis model of the screen pipe was established based on ABAQUS and Python software under pure bending load first. Then, deformation patterns and mechanisms were identified and discussed. The effects of parameters on the screen pipe bending deformation patterns and the ultimate moment were analyzed. Finally, an empirical formula for calculating the ultimate moment of the screen pipe was established. The results showed that the deformation of the screen pipe was complex, and three deformation patterns were related to the hole parameters. Due to an increase in the diameter and number of circumferential and axial holes, the ultimate moment of the screen pipe gradually decreased, and the circumferential holes had a more significant effect on the ultimate moment than the axial holes. The established empirical formula could accurately calculate the ultimate moment of the screen pipe, and the average difference between the formula and numerical simulation results was 3.25%.

Structural Performance of Ferrocement Beams Incorporating Longitudinal Hole Filled with Lightweight Concrete

In this study, 10 ferroconcrete concrete (FC) beams with lightweight cores reinforced with welded steel mesh as a shear reinforcement were evaluated under three-point bending tests along with two conventionally normal-weight concrete (NWC) beams. Expanded polystyrene and lightweight aerated autoclaved brick wastes were used to create lightweight core concrete. The main factors include the type of lightweight concrete used for the core, beam concrete type, the form and number of holes, the existing steel mesh fabric, the hollow, and the hole placement. This study was done on the tested beams' ductility index, failure modes, first cracking loads and associated deflections, and ultimate loads besides corresponding deflections. Experimental results showed that the use of FC, various filling materials, and welded steel meshes in place of traditional stirrups enhanced the ultimate load by 36.6–107.3%, the ultimate deflection by 6–272%, and the ductility by 89–1155% when referenced to a control NWC beam. When the holing ratio increased from 10 to 20%, the ductility of FC beams was enhanced by 307.7%. Proposed equations were developed to predict the ultimate load and bending moment capacity of FC beams while taking into account the compressive strength of the beam body and filling material, the holing ratio, the tensile reinforcement ratio, and the volume fraction of the steel mesh.

Seismic performance of bolted connection between T-shaped section column and I-section beam with L-stubs

Bolted beam-to-column connections can reduce the construction period and are proper for prefabricated structures. Based on the traditional bolted connections, a beam-to-column bolted joint with L-stubs was proposed to connect the I-section beam and T-shaped section column using only bolts on site. Changing the parameters of L-stub end plate thickness, stiffener layouts, friction coefficient, column web thickness and the quantity of the beam flange bolts, experimental and numerical investigations were conducted on the cyclic performances of the proposed joint, and the hysteretic curve, skeleton curve, deformation characteristics, ductility and rotational capacity, as well as the slipping, yield and ultimate resistances, were analyzed. According to the results, the proposed joint can perform as a rigid joint without slipping under small earthquakes, and develop considerable ductility and energy dissipation ability under moderate or large earthquakes by slipping and plastic deformations. Increasing the friction coefficient can improve the slipping moment, and the stiffeners can improve the joints stiffness. The joint energy dissipation capacity could be increased by adding bolts. Based on the analysis, recommended parameter values for the joints were provided, and simplified formulas were proposed to calculate the slipping, yield and ultimate moment resistances, providing satisfactory accuracy when compared to the test and finite element results.

Structural performance of orthotropic Steel-Concrete continuous composite decks with larger U-ribs and PBL shear connectors

This study investigates the structural performance of the OSCCCDs with larger U-ribs and PBL shear connectors. Four OSCCCDs with larger U-ribs and PBL shear connector specimens were fabricated and tested under a static load, in which the experimental parameters were the spacing of the PBL shear connector and the spacing of the holes of the PBL shear connectors. Parametric analysis via finite element models was also carried out to explore the effects of the reinforcement ratio, the thickness of the steel plate, the thickness of the U-ribs, the thickness of the concrete slab, and the hole diameter of the PBL shear connector on the structural performance. It can be concluded from the experimental and numerical results that the OSCCCDs exhibited higher bearing capacity and better ductility. The OSCCCDs exhibited flexure failure at the mid-span and diagonal tension failure at the intermediate supports. The thickness of the U-ribs and the thickness of the concrete slab showed the highest impact on the initial stiffness and ultimate load of the OSCCCDs, followed by the spacing of the PBL shear connectors and the spacing of holes in the PBL shear connectors. The reinforcement ratio, the thickness of the steel plate, and the hole diameter of the PBL shear connector had little influence on the initial stiffness and ultimate load of the OSCCCDs. Finally, a simplified flexural analysis method can be proposed to accurately predict the elastic deflection and ultimate bending moment of the OSCCCDs under the service loads, respectively. The maximum absolute discrepancies of the elastic deflection and ultimate bending moment of the theoretical results are 8.2% and 12.0% by validating against the experimental and numerical results within the investigated ranges of parameters, respectively.

Bending Moment of Mortise-and-Tenon Joints in a Crossed Chair Base

This paper investigated the bending moment of chair base joints. The ultimate bending moments (maximum moment), calculated on the base of the measured maximum applied loads (maximum force), were compared for the front leg and rear leg joints of a chair base. The joints had different angles between the stretcher and the leg (joint angle) as well different tenon lengths (30 mm and 32 mm). The results of the tests indicated that for different test specimen configurations but the same tenon-and-mortise geometry, the maximum force of joints with a smaller value of joint angle (front leg joints) was higher than the force values of joints with a larger angle (rear leg joints) for all tenon lengths. However, the results showed less difference among the calculated bending moments of the analysed sets of joints. A significant difference was not revealed between the bending moments of joints with a smaller value of joint angle and the bending moments of joints with a larger angle for all tenon lengths. A significant difference between the bending moments for the tenon length of 30 mm and tenon length of 32 mm was determined for rear leg joints but not for front leg joints. The presented approach of joint strength analysis through the testing of specimens with different shapes and dimensions are applicable to research and practice.

One pre-stressed methodology named as swelling-fit for binderless dowels joint of wood

One methodology of binderless joint by swelling of dowels with very low moisture content to obtain pre-stress for fast-growing timber was proposed in this paper. The results showed that performance of binderless joint after 48 h conditioning was close to traditional glued-joint, that is 31.5 N·m for ultimate bending moment capacity and 1743.4 N for maximum withdrawing force of two-pin joint. Clear densification of intersection between dowels and poplar beams was observed from micro-structure analysis. The theoretical model to predict the maximum withdrawal force of pre-stressed joint was setup, which is in coincidence with test results.

Estimation of blast-induced peak response of concrete-filled double-skin tube columns by intelligence-based technique

This paper aims to predict the peak response of concrete-filled steel tubes (CFSTs) under blast loads using regression-based machine learning (ML) algorithms considering the variability of input parameters. Twelve regression metrics that are commonly used are utilized to evaluate and compare the efficiency and effectiveness of the proposed ML models. The Monte Carlo approach is used to propagate the variability in the input space to the predicted output. The results showed that the optimal method varies with perspectives. The XGBoost algorithm has the highest final score, and the SVM algorithm exhibits the highest total score for standard deviation. Furthermore, the confidence interval increases with the peak response, and the single model presents a higher accuracy in predicting large displacements. However, ensemble models do the opposite. Sensitivity and uncertainty analyses are performed, indicating that the scaled distance, section size and ultimate moment capacity exhibit the highest contribution to the peak response of the CFST. Finally, a simple formula is developed based on the MLP model, which can cover three input parameters. The findings of this paper can be used for computer-aided dynamic response design of CFST columns subjected to blast loads.

Experimental and numerical study on the prefabricated double L-shaped beam-column joint with triangular stiffener

This study proposes an innovative prefabricated double L-shaped beam-column joint with triangular stiffener (double L-shaped joint) for low-rise residential buildings. The double L-shaped joint consists of the L-shaped connector with triangular stiffener, web side plate connection, H-shaped beam, and concrete-filled lightweight steel tube (CFLST) column or square hollow steel tube (SHS) column. Twelve double L-shaped joints are manufactured and experimented. The design parameters include the column types (CFLST or SHS), triangular stiffener height, perforated end plate (with or without), and the web side plate connection (with or without). In addition, the failure modes, hysteretic performances, ultimate capacity, stiffness degradation, deformation capacity, energy dissipation, and strain responses of joint specimens are analyzed. The experimental results show that the failure modes include steel tube local buckling, weld cracking, and bolts fracture in the area of the L-shaped connector. The ultimate moment of the CFLST column joints rises from 4.53% to 13.05% compared to the SHS column joints, while the initial stiffness increases from 2.16% to 26.46%. The perforated end plate grows at the ultimate moment, but the ductility index reduces. The initial stiffness and deformation capacity of the specimens without a web side plate connection decreases significantly. The finite element model is developed, and the numerical simulation is conducted. The experimental results are consistent with failure modes and bending moment versus rotation angle curves obtioned by numerical simulation.

Experimental study on flexural behavior of full-scale retard-bonded prestressed UHPC variable section cantilever beams

Ultra high performance concrete (UHPC) cantilever beams are firstly used as the main load-bearing components in an open-air spiral staircase of a grand opera house under construction. In order to achieve the requirements of light weight, long span, good durability and strong bearing capacity, UHPC and retard-bonded prestressed tendon (RPBT) are combined in the cantilever beam with π-shaped section that varies along the length of the beam. In order to study the flexural behavior of the cantilever beam and provide reference for the design, through the experiment on flexural behavior of two full-scale (15.04 m long) retard-bonded prestressed UHPC variable section cantilever beams, the failure phenomenon, crack distribution, stress development of UHPC and steel bars, and prestress increment were studied. The test results show that each variable section cracked in turn. The failure section is 2.6 m away from the beam root. After unloading, the deflection recovery (87.8 % of the maximum deformation) was obvious, the prestress did not fail. The beam had good bearing capacity and ductility. For the beam with variable sections, it is necessary to determine the cracking and failure section firstly. The calculation models of the cracking bending moment Mcr and the ultimate bending moment Mu are established, which are in good agreement with the experimental results. The role of structural plates should be considered in the model due to the particularity of π-shaped section. For further exploration, It is found that the restimate of the flexural capacity is related to the the ratio of compression zone height to section height x/h in the existing design codes. The smaller the x/h is, the flexural capacity will be underestimated. However, the proposed model can well estimate the flexural capacity, which is in better agreement with the existing experimental results than the design codes.

Overall stability behavior and design method of Q460 high strength steel welded I-section overhanging beams

To investigate the overall stability behavior of Q460 high strength steel (HSS) welded I-section overhanging beams and develop the corresponding design method of codified specifications, nine overhanging beams with various top flange strengthened section forms and overhanging span length ratios were tested under concentrated loads. The initial geometric imperfections and residual stresses were measured in advance. Test results indicate that the overall stability capacity of the specimens decreases with the increase of overhanging span length ratio and top flange strengthened has a greater effect on the overall stability capacity of overhanging beams than overhanging span length ratio when the dominative stability segment of specimens is located at the simply supported span. Finite element analysis (FEA) models verified by test results were established to examine the effects of load form, load ratio, section form, height-to-width ratio, simply supported span length and overhanging span length ratio on the overall stability capacity of Q460 HSS welded I-section overhanging beams. On the basis of the eigenvalue buckling analysis results and the formulas for the elastic moment of simply supported beam stipulated in Design code of steel structures (GB50017-2017), the calculation formulas of elastic critical moment for overhanging beams were obtained by regression. Furthermore, the calculation formulas of ultimate bending moment for Q460 HSS welded I-section overhanging beams were proposed based on the obtained formulas for elastic critical moment of such beams, test results and nonlinear buckling analysis results.