Service Loading Conditions Research Articles

Strengthening of Garudchatti bridge after failure of Chauras bridge

Two continuous lattice steel truss bridges spanning 190m with subdivided top chord members were constructed on the same design across river Alaknanda at Dugadda and Srinagar, respectively, in Uttarakhand, India. Both bridges were similar in design and geometry having middle span of 110.0m and two end spans of 40.0m. Garudchatti bridge at Dugadda was constructed first and opened to traffic, but excessive vibrations and lifting of end supports under live load condition were observed. Construction of Chauras bridge at Srinagar started later, but it collapsed during casting of the deck slab due to buckling of one of its top chord compression members. Failure of Chauras bridge led to the serious concerns in the minds of people and technocrats about the safety of Garudchatti bridge also, because it was constructed using the same design of Chauras bridge. Therefore, it was decided to strengthen and carry out load testing of Garudchatti bridge before reopening to the traffic.In the present work analyses of Garudchatti bridge are presented to identify structurally unsafe members for most severe live loads given in IRC:6-2010 code, and recommendations for strengthening of the critical members. Finite element space frame analyses of the bridge were carried out using STAAD Pro. v8i software to find excessively stressed members beyond their permissible stress limit. The critical compression members were strengthened by welding additional channel sections. RCC anchor blocks were constructed to restrict lifting of end supports under live load. After strengthening, load testing of the bridge was performed to ensure the safety of the bridge. The bridge is now reopened for traffic.In the past a number of bridges have collapsed during load testing. In case of any shortcoming in the design or overloading during load testing, compression members of the truss may suddenly buckle and cause collapse of the bridge. Therefore, it is not advisable to load test steel truss bridges which do not have adequate margin beyond the service load condition.

Advanced Active Prestressed CFRP in RCC Structures

. The need for rehabilitation of reinforced concrete structures is rapidly increasing. Fibre reinforced polymer (FRP) composite materials for concrete structures have high strength-to-weight ratios that can provide high prestressing forces while adding minimal additional weight to a structure. They also have good fatigue properties and exhibit low relaxation losses, both of which can increase the service lives and the load carrying capacities of reinforced concrete structures. Carbon fiber reinforced polymer (CFRP) composite system is integrated system based on carbon fibres and epoxy resins. By prestressing the CFRP laminates, the material is used more efficiently as a part of its tensile capacity is utilised and it contributes to the load bearing capacity under both service and ultimate load condition. This is an ideal technique as it combines the advantage of using noncorrosive and lightweight advanced composite material in the form of FRP laminates with high efficiency offered by external prestressing. An innovative mechanical anchorage system was developed to prestress the FRP laminates directly by jacking and reacting against the RCC structure.This paper describes the use of Prestressed CFRP laminates for strengthening of RCC structures including practical applications on slabs and bridges. Also it elucidates the post strengthening testing carried out for the validation of this technique.

강섬유보강 콘크리트를 사용한 무배근 연속슬래브의 구조성능

Slab is one of the most important members in the building structures because it covers the largest area of the building. But, amount of reinforcement in this member is relatively small because of its small supporting loads. And large exposed area in slab can induce the cracks. To improve this characteristics, the new slab system consist of structural deck-plate and fiber reinforced concrete was suggested for improving construction ability and reduction of construction period. Basic concept of this slab system is that structural deck-plate can replace the tensile reinforcing bars and concrete form, and fiber reinforced concrete can replace the temperature reinforcement. But, previous study was limited because it tested only simply supported slab specimens. This study tested various continuous slab specimens to find the applicability of the suggested new slab system without any additional reinforcement. Design concept is that structural design of slab is assumed as simply support slab, but it should keep the negative moment cracks under allowable crack width in service load conditions. Four continuous slab specimens in total were tested for analyzing the flexural strength, stiffness, deflection, crack development and failure pattern. Test results indicated that suggested new slab system appeared to be better flexural capacity and stiffness than normal reinforced concrete slab with negative moment reinforcement. And it can control the cracks under the allowable crack width upto the service and factored loads.

An efficient computational approach to evaluate the ratcheting performance of rail steels under cyclic rolling contact in service

A comprehensive study was carried out to numerically evaluate the ratcheting performance of three high strength pearlitic rail steels under different wheel–rail cyclic rolling contact conditions, i.e. free rolling, partial slip, and full slip conditions, different friction coefficients and different axle loads. The wheel–rail cyclic rolling contact was simulated by repeatedly passing a distributed contact pressure and a distributed tangential traction on the rail surface. This study combined the non-Hertzian contact pressure from finite element analysis with the longitudinal tangential traction from Carter’s theory to simulate the wheel–rail cyclic rolling contact problems. A cyclic plasticity material model considering the non-proportionally loading effect developed recently by the authors was applied to simulate the ratcheting behaviour of rail steels. The ratcheting performance of the rail steels was evaluated by the crack initiation life which was determined from the stabilized ratcheting strain rate and the ductility limit of the rail materials. The numerical results indicate that the crack initiation life decreases with the increase of the normalized tangential traction, the friction coefficient and the axle load for all three rail steels. Among the three rail steels, the hypereutectoid rail steel grade with a lower carbon content provides the best ratcheting performance under higher axle loads such as those used railway transport of mineral products in Australia. Furthermore, the numerical results obtained in this study are in reasonable agreement with the in-service performance of the three rail steels. This indicates that the developed approach has the capacity to evaluate the ratcheting performance of other rail steels under service loading conditions. The outcomes can provide useful information to the development and application of rail steels and the development of effective rail maintenance strategies in order to mitigate rail degradation.

Investigation of the Residual Stress State in an Epoxy Based Specimen

Process induced residual stresses may play an important role under service loading conditions for fiber reinforced composite. They may initiate premature cracks and alter the internal stress level. Therefore, the developed numerical models have to be validated with the experimental observations. In the present work, the formation of the residual stresses/strains are captured from experimental measurements and numerical models. An epoxy/steel based sample configuration is considered which creates an in-plane biaxial stress state during curing of the resin. A hole drilling process with a diameter of 5 mm is subsequently applied to the specimen and the released strains after drilling are measured using the Digital Image Correlation (DIC) technique. The material characterization of the utilized epoxy material is obtained from the experimental tests such as differential scanning calorimetry (DSC) for the curing behavior, dynamic mechanical analysis (DMA) for the elastic modulus evolution during the process and a thermo-mechanical analysis (TMA) for the coefficient of thermal expansion (CTE) and curing shrinkage. A numerical process model is also developed by taking the constitutive material models, i.e. cure kinetics, elastic modulus, CTE, chemical shrinkage, etc. together with the drilling process using the finite element method. The measured and predicted in-plane residual strain states are compared for the epoxy/metal biaxial stress specimen.

Experimental Study of Mechanical Behavior of HPL Composites

The paper provides experimental results from tensile and flexural tests of HPL composites. Mechanical properties of HPL laminates from four worldwide producers (Fundermax, Polyrey, Abet and Rexin) are compared. Composites are compared due to their stiffness and strength, both tensile and flexural. The exterior environment effect on mechanical behaviour of composites in service load conditions are presented too.

Partial Prestressed Concrete Slabs as an Alternative for Vehicle Decks of Steel Truss Bridges

Steel truss bridges with continuous reinforced concrete slab as vehicle decks are often found in Indonesia. The use of continuous reinforced concrete slab along the steel truss bridges has still have some problems in the field such as the occurrence of cracks. Cracks that occur on the concrete slab are required to be repaired, which is mostly done by grouting method. However, the method are still unsuccessful in addition to costly expensive.Study on partial prestressed concrete slab as vehicle decks of steel truss bridge was done. The system used was a partial prestressed concrete segmental slab in one direction which was set transversely the bridge. Two concrete slab specimens were cast which had a length of 7000mm, a width of 1000mm and a height of 250mm, respectively. Symmetrical reinforcement consists of four non-prestressed steel bars and three strands, placed on the top and bottom sides of the slab. The steel bars have a diameter of 18mm and the strands have a diameter of 0.5 inches. Plain steel bars with a diameter of 10mm were used as stirrups, spacing at 200mm. The slabs were then tested in the laboratory with a gradual loading increament. At every stage of loading, crack width and strain of steel reinforcement were measured.The test results showed that at the service load condition according to the BMS standard, no cracks was occurred on the concrete slab and the non-prestressed reinforcing steels were still under compression. At maximum load condition, cracks occurred evenly spaced at 85,5mm to 112,5mm and a maximum crack width was 3.2mm. Based on the test results, it can be concluded that such partial prestressed concrete segmental slab was very good to be used as an alternative for the vehicle decks of steel truss bridges.

Computational analysis of gear-box roller-bearing white-etch cracking

Purpose – A simple economic analysis has revealed that in order for wind energy to be a viable alternative, wind-turbines (convertors of wind energy into electrical energy) must be able to operate for at least 20 years, with only regular maintenance. However, wind-turbines built nowadays do not generally possess this level of reliability and durability. Specifically, due to the malfunction and failure of drive-trains/gear-boxes, many wind-turbines require major repairs after only three to five years in service. The paper aims to discuss these issues. Design/methodology/approach – The subject of the present work is the so-called white etch cracking, one of the key processes responsible for the premature failure of gear-box roller-bearings. To address this problem, a multi-physics computational methodology is developed and used to analyze the problem of wind-turbine gear-box roller-bearing premature-failure. The main components of the proposed methodology include the analyses of: first, hydrogen dissolution and the accompanying grain-boundary embrittlement phenomena; second, hydrogen diffusion from the crack-wake into the adjacent unfractured material; third, the inter-granular fracture processes; and fourth, the kinematic and structural response of the bearing under service-loading conditions. Findings – The results obtained clearly revealed the operation of the white-etch cracking phenomenon in wind-turbine gear-box roller-bearings and its dependence on the attendant loading and environmental conditions. Originality/value – The present work attempts to make a contribution to the resolution of an important problem related to premature-failure and inferior reliability of wind-turbine gearboxes.

Discussion of “Behavior of Coupling Band Joints in Buried Corrugated Steel Pipelines” by David Becerril García and Ian D. Moore

Discussion of “Behavior of Coupling Band Joints in Buried Corrugated Steel Pipelines” by David Becerril García and Ian D. Moore

Application of EWK and Modified X-W Fracture Models to Load-Bearing Lug Joints

In the aeronautic field, ductile structure usually undergoes local fracture under complicated service loading conditions, which may triggers collapse of a structure. As a result, it is very essential to study the mechanism of fracture initiation and propagation of ductile materials especially under complex stress states. In this paper, a comparative study of fracture patterns of a load-bearing lug joints structure under several loading conditions with two ductile fracture models is performed by using the commercial finite element platform ABAQUS/ Explicit through a user material subroutine VUMAT. The numerical comparisons using two ductile fracture models in predicting failure of load-bearing lug joints structure shows that modified X-W fracture model agrees well with the experimental observation under complex stress states.

Fire behavior of concrete T-beams strengthened with near-surface mounted FRP reinforcement

This paper presents results from experimental and numerical studies on fire behavior of reinforced concrete (RC) T-beams strengthened with near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. Four RC T-beams, strengthened with NSM FRP reinforcement, were tested by subjecting them to ASTM E119 standard fire exposure and service load conditions. The test variables included load level, restraint conditions, and fire protection applied on the beams. Data from fire resistance experiments is utilized to validate predictions from numerical model to trace the fire response of NSM FRP strengthened concrete T-beams. Results from fire tests and numerical studies indicate that NSM FRP strengthened beams can sustain service loads for three hours under standard fire conditions, even without any external fire protection. In addition, fire induced axial restraint enhances the fire response of NSM FRP strengthened RC beams, while higher load levels lead to much larger deflections and lower fire resistance in these beams.

Multiphysics computational analysis of white-etch cracking failure mode in wind turbine gearbox bearings

Wind energy is currently one of the most promising and the fastest-growing installed alternative-energy production technologies. It is anticipated that by 2030, at least 20% of the US energy needs will be provided by this form of energy. The economics of wind energy require that wind turbines (convertors of wind energy into electrical energy) be able to operate for at least 20 years, with only regular maintenance. Unfortunately, many wind turbines require major repairs after only 3–5 years in service, mainly due to the failure of their gear boxes. It is this lack of gear box reliability which is currently compromising wind energy economics. In the present work, a multiphysics computational methodology has been developed and used to analyze the problem of white-etch cracking, one of the key processes responsible for the premature failure of gearbox roller bearings. The multiphysics methodology includes: (a) quantum-mechanical calculations of the hydrogen dissolution and the accompanying grain boundary embrittlement phenomena; (b) atomistic-level kinetic Monte Carlo analysis of hydrogen diffusion from the crack wake into the adjacent unfractured material; (c) cohesive zone type modeling of the intergranular fracture processes; and (d) a conventional displacement-based finite element analysis of the kinematic and structural response of the bearing under service loading conditions. The results obtained clearly revealed the operation of the white-etch cracking phenomena and their possible interaction with the conventional rolling-contact fatigue damage processes.

STRESS ANALYSIS AND FATIGUE LIFE PREDICTION OF WING- FUSELAGE LUG JOINT ATTACHMENT BRACKET OF A TRANSPORT AIRCRAFT

Civil transport aircraft is used for ferrying passengers from one place to another. Aircraft is a highly complex flying structure. Generally transport aircraft undergoes nominal maneuring flights. During the flight when the maximum lift is generated, the wings of the aircraft will undergo highest bending moment. The bending moment will be maximum at the root of the wing which caused highest stress at this location. Wings are attached to the fuselage structure through wing-fuselage attachment brackets. The bending moment and shear loads from the wing are transferred to the fuselage through the attachment joints. In this project bending load transfer joint is considered for the analysis. First one needs to ensure the static load carrying capability of the wing-fuselage attachment bracket. Stress analysis will be carried out for the given geometry of the wing-fuselage attachment bracket. Finite element method is used for the stress analysis. In the current project, an attempt will be made to predict the fatigue life of wing-fuselage attachment bracket in a transport airframe. In a metallic structure fatigue manifests itself in the form of a crack which propagates. Fatigue cracks will appear at the location of high tensile stress locations. These locations are invariably of high stress concentration. Fatigue life calculation will be carried out for typical service loading condition using constant amplitude S-N data for various stress ratios and local stress history at stress concentration. In this paper for modeling CATIA V5 software is used and for analysis tool MSC/ PATRAN and MSC/ NASTRAN 2010.

Erratum to: “A new accelerated zero-failure test model for rolling bearings under elevated temperature conditions”

A method for accelerated zero-failure testing was proposed for rolling bearings at high operational temperature. The life-load relationship of rolling bearings is combined with the Arrhenius model based on a life-temperature relationship on bearing lubricants to take the temperature effect on bearing life into consideration. Testing duration was calculated to demonstrate at least 90% reliability at a designed rating life of rolling bearings with a given confidence level under the service load and temperature conditions. A step by step procedure for calculating equivalent bearing load and speed was also proposed using a data of load distribution duration of bearings. Finally, an example was given for the case of a deep-groove ball bearing.

Design of axle housing bolted joint by analytical method

Front axle is one of the most critical aggregate of the Tractor. It is critical from the Design standpoint since it endures the most severe load condition in the Tractor. The objective of the study is to analyze the design of the axle housing bolted joint of the front axle for service load conditions. During the redesign the axle housing the bolted joint has been changed therefore we need to analyze the bolted of the axle housing. Improvement of the joint of the axle is a major area to address the large failure rate of the sealing in the paddy land application. The bolted joint connections require proper attention and detailed analysis at the design stage for a fail safe operation in service. The various Empirical formulas are used for design and analysis of bolted joint.

Development and use of a new burner rig facility to mimic service loading conditions of Ni-based single crystal superalloys

Performing representative experiments of in-service operating conditions of Ni-based superalloys used as high pressure turbine blades in aeroengines is a challenging issue due to the complex environmental, mechanical and thermal solicitations encountered by those components. A new burner rig test facility called MAATRE (French acronym for Mechanics and Aerothermics of Cooled Turbine Blades) has been developed at ENSMA – Pprime Institute to mimic as close as possible those operating conditions. This new test bench has been used to perform complex non-isothermal creep tests representative of thermomechanical solicitations seen by some sections of HP turbine blades during engine certification procedure.

Static and Fatigue Behavior of Sandwich Panels with GFRP Skins and Governed by Soft-Core Shear Failure

Sandwich panels composed of glass fiber–reinforced polymer (GFRP) skins and low-density polyurethane core are investigated for potential structural applications such as lightweight insulated roofing or cladding systems. Ten 1,220×318×78-mm panels, including three control specimens, were tested under high-cycle fatigue at maximum load levels of 45–70% of the ultimate static load. Fatigue tests were carried out to failure, thereby enabling the development of the complete fatigue life (S-N) curve and stiffness degradation. Digital imaging correlation was used to map shear deformations and showed that shear contributes about 90% of the deflection. Both static and fatigue failure modes were due to core shear failure. The study showed that fatigue threshold was 37% of the ultimate static capacity, and that to sustain at least 2 million cycles, service load should be limited to 45% of ultimate. The maximum design service live and snow loads, as well as wind load based on the most critical conditions in Canada, were all below the fatigue threshold of the panel. The panels had a strength safety factor of 2.1 relative to the factored maximum design live and snow load, and 6.5 relative to the factored maximum wind load. Deflection limits may govern for some service load conditions, but is not critical when only wind load considered. Stiffness degradation reached a maximum of 15–20%, but residual deflections upon unloading were insignificant.

Performance of bent stirrup and headed glass fibre reinforced polymer bars in concrete structures

An experimental investigation was conducted to evaluate the performance of various types of glass fibre reinforced polymer (GFRP) reinforcement, including bent stirrups and headed bars in concrete structures. Results from 11 large beams (400 mm × 650 mm × 3650 mm) tested in monotonic three-point flexure were selected for this paper; some specimens used GFRP bent-bar stirrups and some used double-headed straight bar shear reinforcement. Based on the results from the tests, specimens reinforced with bent-bar stirrups and specimens with headed-bar shear reinforcement were found to perform similarly up until the calculated flexural failure load. Beyond that, beams reinforced with bent-bar stirrups showed significantly more deformability due to confinement of concrete in flexural compression. Strains measured in the transverse reinforcement were found to exceed the code limitations, in some cases exceeding 200% of the limit prescribed in both CSA S6 and ACI440.1R. It was also found that at loads close to the service conditions, the cracking behaviour was very similar for the beams reinforced with transverse headed bars and bent-bar stirrups. Finally, the concept of hybrid reinforcement systems for controlling deflections and cracking was introduced. Results from the experiments show promise that these systems can better control deflections and cracking at expected service load conditions.

Performance of an AASHTO Beam Bridge Prestressed with CFRP Tendons

Corrosion-induced deterioration of steel RC highway bridges is one of the major distress types that can render a structurally deficient bridge before reaching the design life. One feasible solution to the problem is to replace the conventional steel reinforcement with noncorrosive carbon fiber–reinforced polymer (CFRP) reinforcements. However, the CFRP reinforcement as an internal reinforcement has not been explored in AASHTO-type prestressed concrete beam bridges. AASHTO-type beams have an I-type cross section with a bottom flange, and on integration of the deck slab, the final shape is a bulb-T section. This paper discusses the experimental investigation of a precast prestressed AASHTO control beam and a bridge model. A 12.5-m-long one-third scale AASHTO-type control beam was experimentally investigated for its flexural behavior when reinforced and prestressed with CFRP. Subsequently, a one-third scale bridge model made of five such beams was constructed, instrumented, and tested under both service and ultimate load conditions. As anticipated, the control beam and the bridge model failures were initiated by rupturing of the prestressing CFRP tendons at the bottom layer. The observed flexural response of the bridge model was in close agreement with that of the control beam. As expected, the failure mode was progressive, with extensive cracking of the bridge model, which gives significant warning prior to the ultimate collapse, overcoming issues related to the otherwise brittle behavior of the CFRP-reinforced structures. It is therefore highly recommended to provide the CFRP tendons in different layers along the depth of the beams to effectively address the issues related to brittle failure exhibited by CFRP reinforcements.

SMART Platform for Structural Health Monitoring of Sensorised Stiffened Composite Panels

A SMART Platform is developed based on sensor readings for Structural Health Monitoring of a stiffened composite panel. The platforms main function is divided into three categories: Passive sensing, Active sensing and Optimal sensor positioning. The platform has self-diagnostic capabilities, i.e. prior to its application the health of the sensors and their connection will be checked to avoid any false alarm. Passive sensing results in impact location and force magnitude detection. Active sensing is performed for damage detection. It results in detecting the damage location and severity. Finally the optimal sensor location can be provided given the number of sensors and probability of detection value. This platform is the first step in applying the developed SHM methodologies to real size structures in service load conditions.