Ranjith Dissanayake

New Combined High and Low-Cycle Fatigue Model to Estimate Life of Steel Bridges considering Interaction of High and Low Amplitudes Loadings

A new model is proposed in this paper for the estimation of the life of bridges subject to damage caused by high cycle fatigue combined with low cycle fatigue taking account of the interaction of high and low amplitude loadings. High cycle fatigue is caused by normal routine traffic (low amplitude) loading while low cycle fatigue is caused by extreme (high amplitude) loading situations produced by such as earthquakes. The model mainly consists of a new damage indicator and a new strain-life fatigue curve. Total strain is treated as the damage variable. The proposed model predictions were verified by comparing with fatigue test results for four materials reported in the literature. The proposed model was then applied to estimate the fatigue life of a bridge member subject to combined high and low-cycle fatigue damage caused by normal traffic and by earthquake loadings. The results of the case study, confirm the importance and applicability of the proposed model.

The Impact of the Gigacycle Fatigue on Steel Bridges

Recent studies have proved that there is no fatigue limit for metallic materials; the stress life curve continuously drops even after 107 cycles. However, existing design codes assume that there is a fatigue limit. Therefore, it is important to use appropriate safety factors if existing codes are used for life evaluations. This paper first describes a method to extend high cycle fatigue stress life curves which are developed using tests on small scale specimens, to the gigacycle regime. Then the difference between the stress life curves of small scale specimens and full scale tests related to steel bridges are explained. Finally, the paper presents a case study on a fatigue critical element of a steel railway bridge to show the significance of the gigacycle regime for fatigue life evaluation.

Retrofitting of damaged bridges – the sustainable solution

ABSTRACT Rehabilitation of damaged bridges may be more beneficial than building new bridges. However, proper methods are necessary to assess the level of damages and to verify the fitness of such bridges for further use. In the assessment, there are two important criteria to consider. One is the amount of damage due to fatigue caused by usual past vehicle loading and the other is the magnitude of damage caused by the unexpected actions. The present paper is about a wrought iron bridge damaged by floods. In order to do the assessment, a condition survey was first carried out. Then an analysis was done using a finite element model of the bridge. The model was validated using results of a field loading test. Both static and dynamic loading tests were conducted using a locomotive with six numbers of 13.16-ton axles for five different loading cases to measure the displacement, strain and acceleration at predetermined (critical) members of the bridge. Then the damage in the bridge due to past loading histories and the future fatigue life of the bridge were estimated. Furthermore, using the validated model, the ability of the bridge for higher loading situations was confirmed. The future life was found as 30 years with a factor of safety of 3. The cost estimated for retrofitting work and constructing new reinforced concrete abutments was much less than that for constructing a new bridge. Therefore, it was decided that the rehabilitation of the bridge with necessary retrofitting work is more economical and sustainable than demolishing it and constructing a new one. The bridge is now in use after being repaired, retrofitted and placed on new abutments.

Hardness-Based Non-destructive Method for Developing Location Specific S-N Curves for Fatigue Life Evaluation

This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.

IMPORTANCE OF CONSISTENT CEMENT QUALITY FOR A SUSTAINABLE CONSTRUCTION

The EN and SLS specifications for Portland cement have largely similar provisions on physical and chemical parameters of cement. However, consistency of cement within standards specifications is significantly high and it affect to standard deviation of concrete. In order to obtain good concrete quality, concrete users need to target a low standard deviation of concrete strength. In order to reduce the strength standard deviation of concrete strength, the material properties variations need to be lowered. This paper discusses variation in cement properties from 5 different cement suppliers. Cement from given suppliers varies between batches/ shipments. It is well understood that there are significant differences in mortar strength, chemical composition, fineness, setting times of same cement type (Type 1) from different suppliers. Experiments were conducted with 48 cement samples of 5 different cement suppliers collected over 10 months time from January 2011 to October 2011. It was found that as all cement brands comply with EN and SLS standards. However, coefficients of variation (COVs) of most parameters, especially strength, are significantly high. This paper answers two key questions; are all nominally similar cements the same? Does cement from same supplier always behave consistently? Finally it recommends cement users and specifies a systematic way to select a consistent cement supplier for an economical and sustainable construction.

Detecting and assessment of tsunami building damage using high‐resolution satellite images with GIS data

Purpose – The purpose of this paper is to present a method and results of evaluating damaged building extraction using an object recognition task in pre‐ and post‐tsunami event. The advantage of remote sensing and its applications made it possible to extract damaged building images and vulnerability easement of wide urban areas due to natural disasters.Design/methodology/approach – The proposed approach involves several advanced morphological operators, among which are adaptive transforms with varying size, shape and grey level of the structuring elements. IKONOS‐2 satellite images consisting of pre‐ and post‐2004 Indian Ocean Tsunami site of the Kalmunai area on the East coast of Sri Lanka were used. Morphological operation using structural element are applied for segmented images, then extracted remaining building foot print using random forest classification method. This work extended further the road lines extraction using Hough transform.Findings – The result was investigated using geographic informa...