• Structural Engineering and Mechanics
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• v.19 no.2
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• pp.185-198
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• 2005

In the design of reinforced concrete beams, it is a standard practice to use the yield stress of the steel reinforcement for the evaluation of the flexural strength. However, because of strain hardening, the tensile strength of the steel reinforcement is often substantially higher than the yield stress. Thus, it is a common belief that the actual flexural strength should be higher than the theoretical flexural strength evaluated with strain hardening ignored. The possible increase in flexural strength due to strain hardening is a two-edge sword. In some cases, it may be treated as strength reserve contributing to extra safety. In other cases, it could lead to greater shear demand causing brittle shear failure of the beam or unexpected greater capacity of the beam causing violation of the strong column-weak beam design philosophy. Strain hardening may also have certain effect on the flexural ductility. In this paper, the effects of strain hardening on the post-peak flexural behaviour, particularly the flexural strength and ductility, of reinforced normal- and high-strength concrete beams are studied. The results reveal that the effects of strain hardening could be quite significant when the tension steel ratio is relatively small.

• Computers and Concrete
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• v.22 no.6
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• pp.527-538
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• 2018

Buckling of longitudinal bars is a brittle failure mechanism, often recorded in reinforced concrete (RC) structures after an earthquake. Studies in the literature highlights that it often occurs when steel is in the post elastic range, by inducing a modification of the engineered stress-strain law of steel in compression. A proper evaluation of this effect is of fundamental importance for correctly evaluating capacity and ductility of structures. Significant errors can be obtained in terms of ultimate bending moment and curvature ductility of an RC section if these effects are not accounted, as well as incorrect evaluations are achieved by non-linear static analyses. This paper presents a numerical investigation aiming to evaluate the engineered stress-strain law of reinforcing steel in compression, including second order effects. Non-linear FE analyses are performed under the assumption of local buckling. A role of key parameters is evaluated, making difference between steel with strain hardening or with perfectly plastic behaviour. Comparisons with experimental data available in the literature confirm the accuracy of the achieved results and make it possible to formulate recommendations for design purposes. Finally, comparisons are made with analytical formulations available in the literature and based on obtained results, a modification of the stress-strain law model of Dhakal and Maekawa (2002) is proposed for fitting the numerical predictions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.896-903
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• 2002

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

• Structural Engineering and Mechanics
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• v.14 no.3
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• pp.287-306
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• 2002

The assessment of structural performance of transfer structures under potential seismic actions is presented. Various seismic assessment methodologies are used, with particular emphasis on the accurate modelling of the higher mode effects and the potential development of a soft storey effect in the mega-columns below the transfer plate (TP) level. Those methods include response spectrum analysis (RSA), manual calculation, pushover analysis (POA) and equivalent static load analysis (ESA). The capabilities and limitations of each method are highlighted. The paper aims, firstly, to determine the appropriate seismic assessment methodology for transfer structures using these different approaches, all of which can be undertaken with the resources generally available in a design office. Secondly, the paper highlights and discusses factors influencing the response behaviour of transfer structures, and finally provides a general indication of their seismic vulnerability. The representative Hong Kong building considered in this paper utilises a structural system with coupled shear walls and moment resisting portal-frames, above and below the TP, respectively. By adopting the wind load profile stipulated in the Code of Practice on Wind Effects: Hong Kong-1983, all the structural members are sized and detailed according to the British Standards BS8110 and the current local practices. The seismic displacement demand for the structure, when built on either rock or deep soil sites, was determined in a companion paper. The lateral load-displacement characteristic of the building, determined herein from manual calculation, has indicated that the poor ductility (brittle nature) of the mega-columns, due mainly to the high level of axial pre-compression as found from the analysis, cannot be effectively alleviated solely by increasing the quantity of confinement stirrups. The interstorey drift demands at lower and upper zones caused by seismic actions are found to be substantially higher than those arising from wind loads. The mega-columns supporting the TP and the coupling beams at higher zones are identified to be the most vulnerable components under seismic actions.

• Journal of the Society of Disaster Information
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• v.13 no.1
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• pp.81-88
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• 2017

In this paper, the behaviour of composite steel-CFRP members is studied experimentally and using FE-analysis. The use of advance composite materials in construction for repair and rehabilitation has become a frequent used method in the last decade. FRP composites have many advantages over the traditional technique of steel bonding for a number of reasons: 1. Composites add little or no additional weight to a building, eliminating the need for costly foundation strengthening. 2. FRP composites are very thin (1.2mm to 1.4mm). So there is no loss of floor space and negligible effect over the architectural aspect. 3. FRP composites do not corrode, this makes it long lasting. However, the method is yet to become a mainstream application due to a number of economical and design related issues. Brittle debonding failure, aging effect on bonding, broad based awareness and proper design guidelines are the main concern for future research works. This paper is focused on the ultimate load carrying capacity of the CFRP-strengthened beams and their effect on the deflection and failures modes by varying the amount of CFRP content.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.312-320
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• 2002

It is well-known that when single rock fractures undergo shear displacement, they are influenced by the boundary conditions and fracture roughness. In this case, aperture geometry will change by means of dilation due to the shear displacement. As fractures become the flow paths, fluid flow through rock fractures is affected by the void geometry. In this study, therefore, the influence of roughness on shear behavior of fractures has been investigated, and the resulting hydraulic behavior has been analyzed. In order for this study, a statistical method has been used to generate rough fractures, and they have been adopted into new conceptual models fur fracture shearing and flow calculations. The main contributions of this study are as follows: firstly, fracture shear behavior becomes less brittle with decreasing fracture roughness and increasing normal stress. Then, the characteristics of aperture distribution becomes those of roughness of fractures indicating its hydraulic significance. Finally, it is observed that with decreasing fracture roughness the breakdown of channel flow occurs more slowly.

• Structural Monitoring and Maintenance
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• v.2 no.3
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• pp.269-282
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• 2015

Civil structures should be designed with the lowest cost and longest lifetime possible and without service failure. The efficient and sustainable use of materials in building design and construction has always been at the forefront for civil engineers and environmentalists. Timber is one of the best contenders for these purposes particularly in terms of aesthetics; fire protection; strength-to-weight ratio; acoustic properties and seismic resistance. In recent years, timber has been used in commercial and taller buildings due to these significant advantages. It should be noted that, since the launch of the modern building standards and codes, a number of different structural systems have been developed to stabilise steel or concrete multistorey buildings, however, structural analysis of high-rise and multi-storey timber frame buildings subjected to lateral loads has not yet been fully understood. Additionally, timber degradation can occur as a result of biological decay of the elements and overloading that can result in structural damage. In such structures, the deficient members and joints require strengthening in order to satisfy new code requirements; determine acceptable level of safety; and avoid brittle failure following earthquake actions. This paper investigates performance assessment and damage assessment of older multi-storey timber buildings. One approach is to retrofit the beams in order to increase the ductility of the frame. Experimental studies indicate that Sprayed Fibre Reinforced Polymer (SFRP) repairing/retrofitting not only updates the integrity of the joint, but also increases its strength; stiffness; and ductility in such a way that the joint remains elastic. Non-linear finite element analysis ('pushover') is carried out to study the behaviour of the structure subjected to simulated gravity and lateral loads. A new global index is re-assessed for damage assessment of the plain and SFRP-retrofitted frames using capacity curves obtained from pushover analysis. This study shows that the proposed method is suitable for structural damage assessment of aged timber buildings. Also SFRP retrofitting can potentially improve the performance and load carrying capacity of the structure.

• Structural Engineering and Mechanics
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• v.81 no.1
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• pp.81-91
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• 2022

The effects of interaction between concrete-gypsum interface and edge crack on the failure behavior of the specimens in senicircular bend (SCB) test were studied in the laboratory and also simulated numerically using the discrete element method. Some quarter circular specimens of gypsum and concrete with 5 cm radii and hieghts were separately prepared. Then the semicircular testing specimens were made by attaching one gypsum and one concrete sample to one another using a special glue and one edge crack is produced (in the interface) by do not using the glue in that part of the interface. The tensile strengths of concrete and gypsum samples were separately measured as 2.2 MPa and 1.3 MPa, respectively. during all testing performances a constant loading rate of 0.005 mm/s were stablished. The proposed testing method showed that the mechanism of failure and fracture in the brittle materials were mostly governed by the dimensions and number of discontinuities. The fracture toughnesses of the SCB samples were related to the fracture patterns during the failure processes of these specimens. The tensile behaviour of edge notch was related to the number of induced tensile cracks which were increased by decreasing the joint length. The fracture toughness of samples was constant by increasing the joint length. The failure process and fracture pattern in the notched semi-circular bending specimens were similar for both methods used in this study (i.e., the laboratory tests and the simulation procedure using the particle flow code (PFC2D)).

• Earthquakes and Structures
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• v.25 no.2
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• pp.125-134
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• 2023

In the present work, a new global damage index is proposed for the seismic performance and failure analysis of concrete gravity dams. Unlike the existing indices of concrete structures, this index doesn't need scaling with an ultimate or an upper value. For this purpose, the Beni-Haroun dam in north-eastern Algeria, is considered as a case study, for which an average seismic capacity curve is first evaluated by performing several incremental dynamic analyses. The seismic performance point of the dam is then determined using the N2 method, considering multiple modes and taking into account the stiffness degradation. The seismic demand is obtained from the design spectrum of the Algerian seismic regulations. A series of recorded and artificial accelerograms are used as dynamic loads to evaluate the nonlinear responses of the dam. The nonlinear behaviour of the concrete mass is modelled by using continuum damage mechanics, where material damage is represented by a scalar field damage variable. This modelling, which is suitable for cyclic loading, uses only a single damage parameter to describe the stiffness degradation of the concrete. The hydrodynamic and the sediment pressures are included in the analyses. The obtained results show that the proposed damage index faithfully describes the successive brittle failures of the dam which increase with increasing applied ground accelerations. It is found that minor damage can occur for ground accelerations less than 0.3 g, and complete failure can be caused by accelerations greater than 0.45 g.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.375-391
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• 2022

This paper discussed and analyzed the interfacial stress distribution characteristic of adjacent cracks in Carbon Fiber Reinforced Polymer (CFRP) plate strengthened concrete slabs. One un-strengthened concrete test beam and four CFRP plate-strengthened concrete test beams were designed to carry out four-point flexural tests. The test data shows that the interfacial shear stress between the interface of CFRP plate and concrete can effectively reduce the crack shrinkage of the tensile concrete and reduces the width of crack. The maximum main crack flexural height in pure bending section of the strengthened specimen is smaller than that of the un-strengthened specimen, the CFRP plate improves the rigidity of specimens without brittle failure. The average ultimate bearing capacity of the CFRP-strengthened specimens was increased by 64.3% compared to that without CFRP-strengthen. This indicites that CFRP enhancement measures can effectively improve the ultimate bearing capacity and delay the occurrence of debonding damage. Based on the derivation of mechanical analysis model, the calculation formula of interfacial shear stress between adjacent cracks is proposed. The distributions characteristics of interfacial shear stress between certain crack widths were given. In the intermediate cracking region of pure bending sections, the length of the interfacial softening near the mid-span cracking position gradually increases as the load increases. The CFRP-concrete interface debonding capacity with the larger adjacent crack spacing is lower than that with the smaller adjacent crack spacing. The theoretical calculation results of interfacial bonding shear stress between adjacent cracks have good agreement with the experimental results. The interfacial debonding failure between adjacent cracks in the intermediate cracking region was mainly caused by the root of the main crack. The larger the spacing between adjacent cracks exists, the easier the interfacial debonding failure occurs.