Case Studies in Structural Engineering最新文献

The paper presents the seismic vulnerability analysis of the military dry dock built in 1861 inside the Messina’s harbor. The study appears very important not only for the relevance of the dry dock itself, but also for its social, military and symbolic role. As a first step, the historical documentation about the dry dock delivered by the Military Technical Office, in charge of its maintenance, was thoroughly examined. This activity was fundamental to understand the construction methods, the rehabilitation works executed after the severe earthquake of 1908 and, finally, the works carried out to increase the size of the dry dock in 1950. After this first step, numerical seismic analyses were done with some implemented finite element models (FEM) of the structure. In each FEM, the vertical loads were applied according to the “construction stages” analysis technique, in order to achieve an appropriate representation of the soil stresses around the structure. The analysis results were evaluated according to the Italian design code (NTC 2008) in order to determine the seismic vulnerability of the dry dock.

More than 7000 reinforced concrete (R/C) buildings were destroyed after the Mw 7.8 Pedernales earthquake in Ecuador. In this paper, concrete materials used in such buildings are studied as a possible source of vulnerability. They have been analyzed and tested (lab and SEM). Evidence found confirmed that quality of construction materials is far from acceptable, and construction practices applied were very poor. Use of sea sand caused very high corrosion level in steel bars and mylonitization of coarse aggregates used in concrete produced very low strength materials. Those facts were the main reasons of damage and collapse of thousands of buildings.

Rail authorities all over the world are paying attention to extend the service lives of railway bridges. The famous Miner’s rule employed deterministic or probabilistic fatigue assessment approaches are generally used to predict remaining fatigue life of ageing railway bridges. Under many variable amplitude loading conditions, life predictions have been found to be unreliable since Miner’s rule does not properly take account the loading sequence effect. Therefore, this paper presents a comparison of a new probabilistic fatigue assessment approach with deterministic approach consisting of a new damage indicator, which captures the loading sequence effect of variable amplitude loads more precisely than the Miner’s rule. The comparison is performed by applying both fatigue assessment approaches to predict the remaining fatigue life of an ageing railway bridge. This comparison intends to conclude the possibility of capturing uncertainty behind loading sequence effect by proposed probabilistic fatigue assessment approach. Initially the paper presents the both approaches. Then the proposed approaches are applied to predict the fatigue lives of an ageing railway bridge. Finally predicted fatigue lives are compared and rationality, significance and validity of the proposed approaches are discussed.

In a current study, a new strut effectiveness factor based on Strut-and-Tie Model (STM) is proposed to assess the ultimate shear strength of reinforced concrete (RC) deep beam subjected to dynamic loads. The derivation of the new effectiveness factor of concrete struts is based on Mohr–Coulomb criterion failure. Two types of concrete failure, diagonal splitting and concrete crushing failure modes, are proposed and examined. The modification of the proposed model is simulated in a MATLABSIMULINK environment. The proposed model exhibits efficiency in assessing dynamic shear resistance for deep beams. Moreover, a parametric study is then conducted to examine the effect of flexural reinforcement ratio, transverse reinforcement and shear-span to depth ratio on shear behavior of RC deep beams with consideration of the changes in strain rate. The proposed effectiveness factor is validated by utilizing the experimental results obtained from the literature and shows good accuracy for prediction the shear strength of reinforced concrete deep beams under different loading conditions.

In this study, the material strength of a carbon steel (JIS SS400), which has been used for the penstock of a hydroelectric power plant for about 50 years, is examined. A series of data were obtained and analyzed by measuring the chemical compositions, observing the macro- and micro-structure and conducting tensile tests. The present study revealed that the material strength (0.2% proof strength and ultimate tensile strength) measured at one site can not be regarded as a reliable representative of the entire structure. On the other hand, strong and positive correlation between equivalent carbon content and material strength indicates that measuring the former is an effective and reasonably accurate estimate of the latter. In addition, potential use of nondestructive evaluations, including the Vickers hardness, and their reliability is discussed. In practice, a series of statistical analysis with those valuable field data provides us with the insight on the material strength of long-term used penstock.

Full-scale structural measurements of new and existing railway catenary systems are becoming increasingly important due to continually increasing train speeds and the resulting consequences. Higher speeds lead to increased loads and greater structural dynamic responses, necessitating that both static and dynamic regulations be fulfilled. Sampling directly on railway catenary sections is necessary to assess their structural behaviour. The results can both be analysed directly and be used for validating and/or improving numerical models, which in turn can be used to explore the structural response at higher speeds. This case study presents and explores a newly developed wireless sensor system that includes multiple sensors that can be mounted arbitrarily on any of the wires in a catenary system. All sensors synchronously sample accelerations and rotational velocities over a range of up to 1400 m. This paper shows the results of mounting the developed sensor system and sampling the data of an existing railway catenary section at the Hovin station in Norway. Sampling was performed from both self-excited tests and 140 scheduled train passages. The outputs have been analysed to show that the data can be used to successfully assess railway catenary structural response components.

This paper investigates the behaviour of load-bearing precast wall system (namely the HC Precast System − HCPS) subject to seismicity in Malaysia. Recent tremors felt across the country heeded the call for the need of seismic design guidelines to be implemented. For this study, the design ground acceleration for Malaysia has not been finalized. Throughout the years, several schools of thought that occurred among different researchers pertaining to the value of design ground acceleration, ranging from 0.05 g to 0.1 g. The implications of the selected values can be great especially in designing new buildings or retrofitting existing ones. Thus, linear analysis using Modal Response Spectrum Analysis (MRSA) and nonlinear pushover analysis of representative HCPS were performed for this study. The finite element (FE) model focused particularly on the nonlinear behaviour of the interface between a precast wall and cast in-situ column. Prior to the modal and pushover analyses, the FE model was validated against quasi-static cyclic test results of identical precast system obtained from literature. Differences between the MRSA and pushover approaches are presented and discussed. Performance levels of the structural system were subjected to three levels of design ground acceleration (0.05, 0.075 and 0.1 g) have been included.

Eccentrically Braced Frames (EBFs) have a capability of energy dissipation relying on horizontal link beams in main frame. Use of vertical link (V-EBF) enhances system performance; main frame damaged, easy replaces after earthquake, and it can be rehabilitated minor changes of existing structure. This paper describes experimental and analytical study of the V-EBF system. Experimental results showed that ultimate shear strength of vertical link is more than two times of yielding strength. In analytical model, Kinematic-Isotropic strain hardening for shear, and only Kinematic for moment, showed accurate results with an upper bound for yielding surface to the vertical link.

This paper presents the findings of an internet based survey conducted on members of the UK steel construction industry. The survey was in the form of an online questionnaire that was open from April to October of 2015. The purpose of the survey was to aid the development of a programme of full scale dynamic testing on UK standard simple and/or semi rigid steel connections. The information that was obtained is of use to both the wider academic community and the steel industry itself. Findings of the survey indicate how often tubular box sections are used on projects, the most popular methods of connecting open sections to box sections, preferred choice of fasteners in blind connections, preferred methods of connecting open section beams to open section columns, how often stainless steel bolts are currently being used on construction projects and finally some additional comments on the design of simple and/or semi-rigid connections are presented that were provided by survey respondents.

Linear static analysis with an alternate load path using dynamic amplification factor (DAF) is often used for redundancy and progressive collapse analysis of steel truss bridges to avoid using the more time-consuming dynamic analysis. This study presents an empirical equation to calculate the DAF for this type of analysis against the initial sudden member fracture. Currently, this analysis employs an approximate model with a single degree of freedom to calculate the DAF. With a 5% damping ratio, the constant DAF of 1.854 is used for all types of steel truss bridges. However, this approach is inaccurate because the DAF varies between bridges and with the location of the fractured members as well. Considering some of the approaches developed for building structures but adapting them to steel truss bridges, this paper proposes an empirical equation that allows for the computation of the DAF from the maximum norm stress ${\sigma }_{is}/{\sigma }_{iy}$ in static linear elastic analysis of the damaged model with a member removal. A total of 30 illustrative cases for two typical steel truss bridges are investigated to obtain the data points for the empirical equation. The proposed empirical equation is the enveloped line offset from the best fit line for the data points in illustrative cases.