Withit Pansuk

Life-cycle reliability assessment of reinforced concrete bridges under multiple hazards

Abstract This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.

Evaluating Damaged Concrete Depth in Reinforced Concrete Structures under Different Fire Exposure Times by Means of NDT and DT Techniques

After a severe fire, concrete structures are generally capable of being repaired rather than demolished. To determine whether the fire-damaged structure can be repaired, an assessment of structural integrity must be conducted. In this research, a laboratory assessment of fire-damaged reinforced concrete (RC) slabs was carried out by using Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The study aimed to evaluate the depth of damaged concrete in RC slabs exposed to fire for different periods of time (30, 60, 90 and 120 minutes) based on the correlation between the experimental results of DT and NDT methods. The experiment was conducted with two concrete grades of 24 and 35 MPa. Limestone aggregates were used in this study. The experimental results indicated that 30 minutes of heating time did not show severe effects on reinforced concrete slabs in comparison with the other cases. A damaged concrete layer of 30 – 45 mm was observed for slabs exposed to fire in 60 and 90 minutes. Besides, 24 MPa slabs also showed a lower damage level compared with 35 MPa slabs.

Mechanical properties of oven-dried mortar exposed to high temperature considering different raw material

Concrete structures can be deteriorated in extreme service conditions especially for fire incidents. For the evaluation of the post-fire performance, analytical methods are very powerful and useful. However, widely applicable mechanical models of fire-damaged material have not yet been proposed. To develop such models, the scale of control volume considering strength, stiffness and deformability is one of important factors. This paper presents an experimental study in which visual observations and mechanical properties of oven-dried mortar after exposed to the fire curves of ISO 834 and ASTM E119 for 90 minutes and to be left to cool down in air were conducted. Mortars were made from two different types of fine aggregate and cement. Experimental results indicate that the raw material made mortar is a prominent factor to introduce the different fire damage characteristics. Meanwhile, the mechanical properties of mortar in fire problem are strongly related to temperature that mortars were experienced to.

BIEs for modelling of discontinuities in linear multi-field half-space

This paper presents an efficient and accurate boundary integral equation method for solving a linear, multi-field, half-space containing a surface of discontinuity and subjected to symmetrical and anti-symmetrical conditions on the boundary. Responses of the half-space are governed by a set of linear partial differential equations which are formulated in a general framework allowing the treatment of Laplace equation, linear elasticity problems, and problems involving multi-field materials such as piezoelectric, piezomagnetic, and piezoelectromagnetic solids. In the formulation, a systematic regularization procedure via the integration by parts, symmetrical and anti-symmetrical properties, and special representations of strongly singular and hyper singular kernels is employed to derive a set of singularity-reduced boundary integral relations. A pair of weak-form boundary integral equations involving both the sum and relative crack-face state variable and surface flux across the discontinuity surface is finally established and they contain only weakly singular kernels. A standard symmetric Galerkin boundary element method (SGBEM) is then implemented to solve those weakly singular integral equations for unknown data on the discontinuity surface. In numerical implementations, continuous local interpolation functions are employed in the approximation of solutions and an efficient means for both the kernel evaluation and the numerical integration is adopted to enhance the accuracy and computational efficiency of the developed scheme. The proposed numerical technique is then verified with various, reliable benchmark cases and a selected set of results is presented to demonstrate its capability and robustness.