Reserve Strength Research Articles

Reliability-based design of corrugated web steel girders in shear as per AASHTO LRFD

Despite their successful use in many bridges across several countries around the world, corrugated web steel girders (CWSGs) haven't been yet recognized formally by mainstream design codes and standards. CWSGs can be an economical alternative to conventional welded plate girders; they can achieve higher shear strengths with lesser material usage. Corrugated webs have been demonstrated to carry about half of their ultimate shear strength after buckling, which is an important reserve strength to overcome sudden collapses of bridge structures. The current design practice combines the latest research in the field with engineering judgment with no regard for reliability-based design. In light of the new developments in the field of bridge design and reliability analysis techniques, this paper revisits first the reliability of welded plate girders in shear and verifies their target reliability index and the corresponding resistance factor as per AASHTO LRFD. Then, and in an attempt to prepare the inclusion of CWSGs shear design in AASHTO LRFD, a probabilistic-based calibration procedure is applied to calibrate the resistance factor for bridges having a range of span lengths and girder spacings, with consideration of different average daily truck traffic. A series of sensitivity analyses were carried out in order to quantify the relative contribution of each design parameter to the overall reliability of CWSGs in shear. The findings of this study suggest that, for CWSGs in shear, a resistance factor of 0.95 is appropriate to ensure a reliability level that is consistently close to the target. The sensitivity analysis showed that the web thickness, web depth, and the yield strength of the web's steel material are the most influential parameters on the reliability index of CWSGs.

Life-cycle cost (LCC) based design procedure to determine the optimal design parameters and target reliability under nonlinear deformation for marine installations

ABSTRACT This study proposes a procedure to determine the optimal design parameters and target reliability based on Life cycle cost (LCC) based analysis. An iterative design procedure is performed for different levels of reserve strength ratio (RSR), and LCC is calculated. A case study is carried out for installation of the bottom fixed jacket support structure for offshore wind turbines (OWT) system subjected to extreme loading condition. To determine the ultimate capacity of the structure, static pushover analysis is integrated with the proposed design methodology. An evolutionary based particle swarm algorithm is selected for the structural design optimization of offshore jackets. The RSR evaluated from pushover analysis assists to determine the probability of failure based on the first order reliability method (FORM). Based on a set of LCC values, which are the collective sum of capital expenditure (CAPEX), operational cost (OPEX), and risk cost (RISKEX), the optimal design is reached.

Substantiating the optimization of the load-bearing structure of a hopper car for transporting pellets and hot agglomerate

The strength parameters have been determined for the bearing structure of a hopper car used to transport pellets and hot agglomerate. The calculation was based on a finite element method, implemented in the software COSMOSWorks. Strength reserves of load-bearing elements in a carbody have been determined. In order to reduce material consumption for a carbody, it has been proposed to use pipes with a circular cross-section as the bearing elements. Mathematical modeling was applied to determine the accelerations that act on the optimized bearing structure of a wagon when it is struck at shunting. It has been established that the accelerations that act on the bearing structure of a wagon amount to 42.4 m/s2 (4.3 g). The derived acceleration magnitude was accounted for when calculating the strength of a hopper car's bearing structure. The maximum equivalent stresses in this case reached about 270 MPa and were concentrated in the region where a girder beam interacts with a pivot beam while not exceeding the permissible ones for the grade of steel used in the metallic structure.We have simulated the vertical dynamics of the optimized bearing structure of a hopper car used to transport pellets and hot agglomerate. During calculations, the parameters for a spring suspension of the 18-100 model's undercarriage were taken into consideration. The results of our calculations make it possible to conclude that the accelerations of a hopper car body, as well as undercarriages, are within the allowable limits. In this case, in terms of compliance with the requirements of normative documents, the car ride quality can be described as «excellent».The proposed technical solutions justify the use of round pipes as the load-bearing elements of a hopper car body for transporting pellets and hot agglomerate. In this case, it becomes possible to reduce the hopper car tare by almost 5 % compared to a prototype car. In addition, the introduction of round pipes in the bearing structure of a hopper car could bring down manufacturing costs for railroad car building enterprises.Our study would contribute to the construction of modern structures of hopper cars, as well as to the improved efficiency of railroad transportation

Composites airframe panel design for post-buckling – An experimental investigation

Three series of airframe composite panels with T-stiffener, I-stiffener and J-stiffener are designed and optimized to have the same local skin buckling load and weight. All the panels are designed to undergo local skin buckling between Design Limit Load (DLL) and Design Ultimate Load (DUL), approximately at 120% of DLL to utilize the reserve strength in structures. Additionally, identical panels are designed and fabricated from each series to study the effect of various extrinsic parameters such as disbond, delamination, impact damage and repeated loading to identify the best performing series for post-buckling design. All the panels are tested under compression to demonstrate no onset of damage before DUL. The influence of defects such as disbond, delamination and impact damage on the post-buckling behavior is also demonstrated. One pristine panel of each series is repeatedly loaded 1000 times beyond buckling to determine the onset of damage if any. The panels with I-stiffener and J-stiffener found to be the potential design choices for post-buckling design philosophy due to the high margin between skin buckling and collapse load even in the presence of damage. The results from this study would help in moving closer to the post-buckled composite design philosophy for airframe structure.

Experimental Study of Friction Resistance between Steel and Concrete in Prefabricated Composite Beam with High‐Strength Frictional Bolt

Prefabrication of composites beam reduces the construction time and makes them easily to be assembled, deconstructed, and partially repaired. The use of high‐strength frictional bolt shear connectors can greatly enhance the sustainability of infrastructure. However, researches about the concrete‐steel friction behavior are very limited. To provide a contribution to this area, 21 tests were conducted to measure the friction coefficient and slip stiffness with different concrete strength, steel strength, and surface treatment of steel. An effective finite element model was developed to investigate the ultimate bearing capacity and load‐slip characteristics of bolt shear connection. The accuracy of the proposed finite element model is validated by the tests in this paper. The results demonstrate a positive correlation between concrete strength and friction coefficient and better performance of shot‐blasted steel. It is also proved that high‐strength frictional bolt has a 30% lower bearing capacity but better strength reserve and antiuplifting than the headed stud.

Evaluation of factors contributing to wave-in-deck using pushover analysis for fixed jacket structures

Wave in deck (WID) phenomenon of a wave hitting on the topside for fixed jacket platforms at shallow water condition has been reported as a notable risk to the workability and reliability of these structures. When hydrocarbon from the seabed is extracted for an extended period of time, there might be a reduction in pressure, which allows subsidence to happen. A platform experiencing subsidence promotes the decrease in air gaps, which eventually allows the waves to attack the bottom decks. The impact of the WID generates additional loads to the structure and therefore increases the values of the moment arms. Higher moment arms trigger instability in terms of overturning, which eventually decreases the reserve strength ratio (RSR) values of the structure. The mechanics of WIDs, however, are still not well understood and have not been fully incorporated into the design codes and standards. Therefore, there is a need to revisit the current design codes and standards for platform design optimization. This paper aims at evaluating the effect of RSR values due to WID on four-legged jacket platforms in Malaysia. Base shear values with regards to calibration and modifications of wave characteristics are obtained by numerical simulations. Correspondingly, pushover analysis was conducted to retrieve the RSR. The effects of the contributing factors, namely wave height, wave period, and water depth with regards to the RSR and base shear values, are expected to be analyzed and thoroughly discussed. The work illustrated in this paper is important in optimizing the design life of the existing and aging offshore structures. Outcomes of this research are expected to provide an additional evaluation of the WID mechanics and in return, contribute to the current mitigation strategies in managing the issue.

Effect of Mortar Constraint Conditions on Pullout Behavior of GFRP Soil Nails

Glass fiber reinforced polymer (GFRP) bars are safe, light, and environmentally friendly and, hence, have emerged as desirable alternatives to traditional steel reinforcements in soil nailing wall reinforcement. The loads experienced by GFRP soil nails are transmitted through bonding with mortar and the surrounding soil mass. Constraints of the soil mass on mortar affect the pullout performance of the nails. This paper presents a laboratory test study on the influence of different mortar constraint conditions on the pullout behavior of GFRP soil nails. The results indicated that single loading or cyclic loading has a negligible effect on the failure modes of specimens under different constraints. Therefore, all specimens underwent the same mode of failure, i.e., splitting failure of the mortar. The ultimate pullout force associated with single loading under strong constraint conditions was 77% higher than that under unconstrained conditions, and the anchorage depth increased from 0.6 m to 1.0 m. The load‐slip curves obtained for unconstrained conditions and strong constraint conditions were approximately straight lines and double broken lines, respectively. The ultimate tensile stress of GFRP soil nails exceeds the tensile strength of ordinary steel bars, indicating that these nails have sufficient strength reserve.

Investigation of Working Bodies of the Device for Separation of Fibers Suitable for Spinning from Cotton Waste

It is known that fiber wastes (lint, down and seeds) produced at ginneries contain fibers that are suitable for spinning and can be used in industry, and their separation significantly increases the level of fiber production (1.9% - 2.5%). Based on these analyzes, the study aimed to create a new device that separates long fibers from lint and down. As a result, the amount of fiber output in the enterprise will increase and the enterprise will have significant economic benefits. In addition, the introduction of the device will prevent the addition of long fibers (longer than 16 mm) that can be used in the textile industry to the waste. This article focuses on the creation of a fiber separation device suitable for the treatment and spinning of fibrous waste produced in ginneries. The study theoretically examined the main working bodies of the fiber separation device from waste. Theoretical research is devoted to the study of the strength of the main working body of the fiber separation device−the separating saw drum and its shaft. In the study, the sawdust drum is a more stressed steel coating, and it was found that the strength reserve of this drum is [δТ] = 2.03 (where δТ = 0.8 - 2.5) was found to be. As a result of calculating the resistance of the saw drum shaft to stiffness and vibration, it was determined that the shafts are resistant to vibration under periodic loading and that the oscillation frequency along its axis through the critical rotation frequency is vcr=10.3 Gts.

Corrosion characteristics of carbon steel in solutions of synthetic detergents

Data of corrosion rate are obtained experimentally, values of braking coefficient, protection degree of steel 10 in 3 % aqueous solutions of detergents ML-52, MS-8 and Labomid-203 are calculated. It is found that when the composition of synthetic detergents diethylene tetraborate ammonium (DETA) composition (NH4)2B4O7·2C2H8N2·2H2O concentration of 0.5 % wt., the corrosion rate of carbon steel is significantly reduced, and the values of the braking coefficient and the protection degree increase and reach almost significant values. By removing the potentiodynamic polarization curves, it is shown that in the presence of DETA, the dissolution potentials of steel 10 are shifted to the positive side relative to the potential in the background solutions and the anode process is predominantly slowed down. Corrosion-fatigue tests indicate increase in the coefficient of cyclic strength reserve of carbon steel in aqueous solutions of synthetic detergents with the addition of DETA. The results allow us to recommend the compound diethylene tetraborate ammonium as effective anticorrosive additive to synthetic detergents used to clean parts from technological contaminants in the repair of process metallurgical plants machines.

Determination of destructive forces in a rod-cable arch

The aim of research - comparison the results of the experimental data with the computer modeling the work of the strengthened brick-cable arch. Methods. Experimental and theoretical methods of research. Results. Firstly, the tests on a small desktop models were performed, for the determination the nature of destruction of the construction. During them, it was discovered, that the arch crash is taking place because of the splitting the small size timber bricks, or as the result of the breaking its steel strengthening elements. Further, the computer model of the construction was created with the help of physically and geometrically nonlinear finite elements at LIRA-SAPR PC. The generated model was load by a concentrated force at its top zone, the same one, as it had been during the experiments before. On the results of the calculation, the maximum deformation was received, which are different from the experimental one on a value less then 10%, what suggests the nearness the computer model to the real construction. The highest compressive strengths of the arch and the largest stretching forces of its steel bands were determined during the further analysis of the model. Maximum splitting and stretching forces also were calculated theoretically, according to the formulas of SP 64.13330.2017 and SP 20.13330.2016. It was determined that the timber bricks have more than 7 times reserve of strength, and the steel bands over them - only times, and during the growth of external force, the arch will crash because of its steel sprengel bands breakage. By the results of the research, the calculation algorithm of such kind constructions was generated, at the base of LIRA-SAPR PC. It was recommended first, to determine deformation of the strengthened brick-cable arch, with further checking the timber elements for splitting and steel sprengel elements for maximum permissible stretching. The problem of stability the flat form of deformation for the brickcable arch are the same as for the glued one, because of the tight connection the timber bricks, with elimination their exit from the frontal plane.

System-based calibration of offshore Malaysia environmental action factors for the ISO 19902 PETRONAS offshore fixed platforms

Previously, the action factors, which are generally used in the region of Malaysia is based on the data from the Gulf of Mexico (GoM) or the North Sea, where the environmental condition is much harsher than the offshore Malaysia. Direct application of the high load factors in these regions can result in a waste of economic resources. Based on a reliability-based Load and Resistance Factor Design approach, the current study is carried out for the provision of system-based approach for the calibration of Offshore Malaysia Annex Extreme Environmental Action Factors based on the data from Malaysian waters. With the accessible SEAFINE and HYCOM hindcast database, long-term statistics of extreme environmental load have been derived for six platform locations in Malaysian waters, following the response-based Load Statistics Module (LSM) process. The Generic Load Model (GLM) including the wave-in-deck forces, which has been employed for transferring the wave motion statistics to structural response statistics, is developed in the paper. The structural resistance uncertainty is characterised by the minimum reserve strength ratios (RSRs) derived from a theoretical model that relates with environmental load factor. A structural system reliability analysis based on the FORM method has been performed for a range of minimum values of theoretical RSR for jacket structures fully designed to ISO Code 19902. Partial action factors associated with extreme environmental loads are calibrated to achieve a target reliability level in terms of reliability index.

Dynamic Reliability Analysis of Tower Crane with Wind Loading

The wind-induced dynamic reliability of tower cranes was studied. A linear filter autoregressive (AR) model is used to simulate the time history of multidimensional fluctuating wind samples, and the corresponding wind load is applied to the finite element model of tower crane to analyze the wind vibration response. Based on Poisson process method, wind vibration reliability analysis of tower crane is carried out.The results show that under the action of wind speed of 20m/s, the probability of strength reliability is over 0.99, and the structural strength reserve of this type of tower crane is relatively sufficient; the displacement reliability is 0.98, when the wind speed is large, the displacement reliability decreases obviously, and the stiffness reserve is slightly insufficient.

Post-cracking shear behaviour of concrete beams strengthened with externally prestressed tendons

External prestressing technology has been successfully adopted for enhancing the load-carrying capacity of beams in bridge engineering. Previous studies on the shear behaviour of externally prestressed concrete (EPC) beams mainly focused on the ultimate shear strength. The post-cracking shear behaviour of EPC beams remains unclear. This study aims to investigate the post-cracking shear behaviour of EPC beams. To this end, nine EPC beams with different design parameters were tested to failure. The investigated parameters included the prestressing condition, shear span to depth ratio, shear reinforcement ratio, and bend angle of external tendons. In contrast to reinforced concrete beams, the EPC beams demonstrated shear tension sliding with concrete spalling failure. The applied prestressing increased the concrete shear contribution by 68%. The percentage of the concrete shear contribution out of the total shear strength of the test beams ranged from 45% to 79%. The post-cracking shear strength reserve ability index, defined as the ratio of the shear strength and shear cracking strength, ranged from 1.72 to 2.96 in the EPC beams. A new ductility index, defined as the ratio of the ultimate deflection and the deflection corresponding to first shear cracking, was used to evaluate the post-cracking deformability of EPC beams. The ductility index of the EPC beams ranged from 3.0 to 7.6, indicating considerable post-cracking deformability. The beam’s stiffness at first shear cracking was 39–81% of the beam’s initial stiffness; the beam’s stiffness at the ultimate state was 18–41% of the beam’s initial stiffness. Finally, the current shear provisions were evaluated by the test results.

Yield Line Analysis of Reinforced Concrete Slab Carrying Concentrated Loading

Yield line analysis of reinforced concrete slab, simply supported on two sides perpendicular to the span and free on the other two sides, carrying concentrated load at different locations is carried out by determining the critical failure mechanism and the corresponding equilibrium equation analytically. Such slabs are often encountered in the form of culverts with concentrated vehicular loads. In practice, elastic methods of analysis are used for their analysis. However, the use of yield line analysis can indicate reserve strength which would result in more rational and economical design of such R.C. slabs for heavy concentrated loading. The change in the failure mechanism and the ultimate load-carrying capacity as the aspect ratio of the slab and positive and negative moment carrying capacity of the slab changes is further investigated. Based on the yield line analysis, design charts are prepared which would aid in the economical design of such slabs for concentrated loading.

An experimental study on the flexural behavior of cold-formed steel composite beams

Local buckling instability under compressive stresses is common in cold-formed steel (CFS) members and generally occurs well before the material has reached its yield strength. This results in under-utilization of the cross-section, compared to its full capacity governed by strength failure. Under flexural loading these CFS members possess sufficient inelastic reserve strength up to the ultimate stage. A recent study indicated that plate girders with tubular flanges offer higher flexural and torsional strengths compared to the ones with flat flanges. Upon packing of the tubular compression flange of CFS beams with hard materials like concrete/ timber etc., there will be a substantial delay in early local buckling instabilities, thus improving their load carrying capacity considerably. Although, numerous CFS composite sections have been developed recently, very limited lightweight packing materials have been adopted. The current study presents an experimental investigation carried out on CFS beams with flanges and webs possessing rectangular box geometry, packed with suitable low-cost lightweight packing materials, resulting in novel light-weight CFS composite beams. Four point flexural tests were conducted on these beams with simply supported end conditions. The ultimate strengths, modes of failure, load vs. displacement plots were obtained to study their flexural behavior, in order to evaluate the structural efficiency of the different packing materials. Lastly, the North American Specifications and Australian New Zealand Standard for CFS structures were also used for determining the design strengths of the specimens for comparison sake. This study proved that these novel CFS composite beams have shown better performance considerably.

Comparative Study of Seismic Design and Performance of OMRF Building Using Indian, British, and European Codes

In India, damage cause by some major earthquakes, such as India/Nepal 2015, Sikkim 2011, Kashmir 2005, Bhuj 2001, Latur 1993, and Uttarkashi 1991, have raised alarms to professionals. The probability of seismic risk is higher in more densely populated Indian cities, such as Bhuj, Kashmir, Sikkim, Uttarkashi, as they come under the highest seismicity zone in India. Therefore, our primary interest is to investigate the seismic performance evaluation of the buildings in these seismic prone areas. Significant research has been conducted on the seismic performance of existing buildings. However, investigations on the seismic performance of a building with different country codes for the same earthquake event has not been explored, which is crucial in providing a deeper knowledge of the seismic performance of buildings. This paper presents a comparative study of an Ordinary Moment Resistant Frame (OMRF) building designed using three major codes, Indian (IS: 456-2000, IS: 1893-2002), British (BS: 8110-1997) and European (EC-2, EC-8). Six typical building models considered with earthquake (WiEQ), and without earthquake (WoEQ), and their assessments were interpreted using non-linear static analysis for determining their seismic performance. Seismic performance is compared in terms of base shear coefficient (BSC) and drift ratio that shows WiEQ models, at the drift ratio of 1.5%, the BSC was as follows; 0.78, 0.88, and 0.96 for the models designed for British, Euro, and Indian codes, respectively. The results show that the building models, that have been designed for the Indian codal provisions for both cases, performed well as compared to the other country codes. Base shear and drift ratio are the vital parameters that vary considerably among the building models. This aspect of the Indian code makes it a safer design methodology with higher reserve strength and a reasonably good displacement capacity before reaching the Collapse Prevention (CP) performance level.

A musculoskeletal modelling approach to explain sit-to-stand difficulties in older people due to changes in muscle recruitment and movement strategies

By 2050 the proportion of over 65s is predicted to be 20% of the population. The consequences of an age-related reduction in muscle mass have not been fully investigated and, therefore, the aim of the present study was to quantify the muscle and joint contact forces using musculoskeletal modelling, during a sit-to-stand activity, to better explain difficulties in performing everyday activities for older people. A sit-to-stand activity with and without the use of arm rests was observed in ninety-five male participants, placed into groups of young (aged 18–35 years), middle-aged (aged 40–60 years) or older adults (aged 65 years and over). Older participants demonstrated significantly lower knee extensor and joint forces than the young when not using arm rests, compensating through elevated hip extensor and ankle plantarflexor muscle activity. The older group were also found to have higher shoulder joint contact forces whilst using arm rests. This tendency to reorganise muscle recruitment to include neighbouring groups or other parts of the body could make everyday activities more susceptible to age-related functional decline. Reductions in leg strength, via age- or atrophy- related means, creates increased reliance on the upper body and may result in further lower limb atrophy through disuse. The eventual decline of upper body function reduces strength reserves, leading to increased vulnerability, dependence on others and risk of institutionalisation.

Resistance Exercise for the Prevention and Treatment of Pediatric Dynapenia

Temporal trends of youth muscular fitness (i.e., muscular strength, muscular power and local muscular endurance) indicate that contemporary children and adolescents are weaker and slower than previous generations. Consequently, this generation of millennials appear to be just as vulnerable as older adults to the inevitable consequences of muscle disuse and neuromuscular dysfunction. The modern-day construct of pediatric dynapenia describes an identifiable and treatable condition in youth characterized by low levels of muscular strength and power and consequent physical and psychosocial limitations not caused by neurologic or muscular disease. An interaction of modifiable physical and psychosocial factors can influence the development and progression of pediatric dynapenia. Without structured interventions that target strength deficits and build strength reserves in a supporting environment, the divergence in performance between weaker and stronger children may persist into adolescence because weaker youth may be unable to break through a so-called strength barrier. Regular participation in a well-designed youth resistance training program provides an opportunity for youth to enhance their health and fitness while acquiring the physical skills and behaviors that support an active lifestyle. New insights have highlighted the importance of initiating strength-building interventions early in life to optimize performance gains in other important components of physical fitness. Developmentally appropriate resistance training should be integrated into school- and community-based youth fitness programs and strength-building activities should take a more prominent position in public health physical activity recommendations for children and adolescents.

A new buckling-restrained brace with gap-supported tendon protection: Experiment and application

For the Buckling-Restrained Braced Frame (BRBF), the reserve strength is critical to reduce maximum and residual drifts, and improve the collapse prevention margin. In this paper, a newly proposed brace is named TP-BRB, which is composed of a Buckling-Restrained Brace (BRB) and a gap-supported Tendon Protection in parallel. Instead of the conventional BRB, the TP-BRB is designed to provide additional stiffness and strength for steel frames after the axial deformation of TP-BRB reaches a threshold value. A quasi-static test of the TP-BRB was conducted to confirm the excellent performance of the new configuration and calibrate the numerical model in OpenSees. Nonlinear time-history analyses were performed to compare the responses of the TP-BRB frame and BRB frame models. The results show that replacing BRB with TP-BRB is an effective means to reduce the maximum and residual story drifts, and increase the collapse prevention margin under strong earthquake; moreover, it reduces the BRB deformation demands without reducing of the energy dissipation capacity of steel frames.

Experimental Study on the Global Stability of the xiaowan Arch Dam Using a 3D Geo-mechanical Model Test

In this paper, a three-dimensional geo-mechanical model test for the Xiaowan high arch dam was studied and the topographical and geological features, the distribution of weak structural planes, the shallow relaxation unloading phenomena were simulated. Furthermore, a type of model material known as the temperature analogous material, whose strength varies with temperature throughout the experiment, was used to simulate the decrease in shear strength of the weak structural planes. The deformation characteristics and failure mechanism of the dam foundation and abutments were obtained by using comprehensive test method, which considered both the overloading and strength-reduction techniques. Through data analysis, the strength reserve coefficient, the overloading and the global safety factor were obtained. Synthetic analysis of the test results indicates that the displacement of the mid-upper abutment was reduced and the failure zone become smaller due to the significant reinforcement effects of concrete displacement plugs on the faults and alteration zones. The failure pattern shown in the model test indicates that reinforcements should be installed at faults F11 and F10 above an elevation of 1245 m in the right abutment and the rock above the thrust block in the left abutment.