International Journal of Civil Engineering
Volume:16 Issue: 7, Jul 2018

The aim of this study is to determine the causes of brittle collapse of existing reinforced concrete (RC) flat slab supported by columns under vertical loading. This paper focuses on the assessment of RC flat slab structures from the point of punching shear resistance. The entire process is illustrated using a case study from a parking structure. In the examined structure, the second storey slab was collapsed to the first storey slab without any earthquake and impact effects. A partially collapsed RC flat slab structure is examined within the scope of a field survey, lab studies, and numerical analyses. The first stage of the study examines the existing state of the collapsed structure and its compliance with architectural and structural drawings. Second, mechanical tests are conducted on samples gathered from the structure, based on observational research and lab environment. At the final stage, the structure’s three-dimensional finite element model is prepared and the causes of the collapse of the structure are determined. The analysis shows that the lack of shear reinforcement, unforeseen loadings, and design errors are remarkably harmful to the slab–column connection resulting in punching shear resistance.

The study of the reinforced concrete (RC) columns’ response to horizontal loads is of full importance to understand how earthquakes affect the integrity of structures, essentially those already built and especially vulnerable to this type of action, as is the case with many existing buildings on significant seismic activity zones which are not adequately prepared for that eventuality. Consequently, there is also the need to perform a significant number of experimental and numerical studies to understand how much the columns resistance is affected by the horizontal loading path combined with axial load. The present study focus on the comparison between the RC columns response when subjected to uniaxial and biaxial loading through a literature review of the experimental test data results. Additionally, a parametric study was performed to analyze the load-path influence in the columns response. Non-linear static pushover analysis were performed in more than 36 columns with different cross-sections, reinforcement ratios and axial load ratio, performing a total of 1300 analysis. The numerical results will be presented in terms of capacity curves, maximum strength comparison between the uniaxial and the biaxial response and several ratios were also determined to a do a better comparison.

Masonry structures have been widely used in residences and in commercial and public buildings around the world. Most existing masonry structures have asymmetric damages that significantly influence their safety in earthquakes. Their seismic assessment would not be reliable without considering the influences of these asymmetric damages. To address the issue, the authors conduct a pseudo-static test on a masonry model with asymmetric damages. Before the test, the authors apply asymmetric damages by weakening one of the load-bearing walls of the model. In the test, the authors apply synchronized horizontal displacements on top of the load-bearing walls in a cyclical manner, and record the deformation, crack distributions, and reaction forces. Based on the records, the authors analyze the deformation patterns, failure procedure, cracking pattern, hysteretic behaviors, and stiffness degradation of the model. The test results indicate that asymmetric damages cause nontrivial structural rotation under horizontal loading, and then make the walls fail in different patterns. The structural rotation significantly influences the distribution of the seismic internal forces. Excluding the rotation in the calculation, one can underestimate the seismic internal forces for walls without damages and overestimate the forces for walls with damages. The structural rotation also influences the seismic strengthening scheme. One should apply strengthening measures both in the member scale and in the structural scale. The findings can be referred to in seismic assessment for most existing masonry structures.

City design involves various parameters such as appropriate positioning of municipal facilities, residential regions, and public centers. When a city is faced with a disaster, it should be robust enough to minimize the rate of fatalities. In this line, emergency relief and urgent evacuation are among the key activities shall be addressed for an emergency management strategy. This paper focuses on the design of an assumed city when evacuation action after earthquake is directly addressed. For doing this, key risks associated with evacuation activities are first identified. The identified risks are then analyzed using fault tree techniques. Defining risk criteria between 0.1 and 0.9—where 0.1 means low risk, 0.1–0.3 means acceptable risk, 0.3–0.6 means considerable risk and more than 0.6 means extremely high risk—it is thus understood whether the risk are acceptable. The city is then designed in a way when an evacuation activity is required to performed; the risk associated becomes in an acceptable range. To do this, three distinct zones with different residential and public centers are positioned within the boundary of the city based on which the locations and directions of the connective routes are set up. The results show that the risk of the city based on evacuation is as low as 0.28, which is within the acceptable criterion.

In this paper, the seismic response of recycled aggregate concrete (RAC) frames was investigated through the bidirectional shaking table test for a three-storey RAC frame model with 1:4 reduced scale. According to test results, the variation regularity of the structural frequency, damping, and the inter-storey displacement angle was analyzed, which illustrated a good seismic behavior of this RAC framework. Furthermore, a damage model of the corresponding RAC integral structure was proposed with a comprehensive consideration of the different frequencies in X and Y directions, damping ratio, stiffness, vibration mode of the structure, variety of structure forms, and test methods for natural frequency. Based on the damage model for the RAC structure, the damage grade was analyzed. Meanwhile, combined with the classification of earthquake damage to buildings and special structures, code for seismic design of buildings (GB50011-2010), and other literature, a standard with five damage grades of the RAC structure was established. At last, to apply for practical engineering, a quick computational formula for RAC structure damage index was fitted. The results obtained from the previous studies indicate that the damage model is basically consistent with the experimental results and is capable of applying into seismic damage quantitative evaluations and analyses for actual RAC structures.

To improve the structural seismic response of liquid storage tanks, in the last 50 years, many researchers have developed different mathematical models, ranging from those based on discrete elements such as simplified two-mass models to those involving fluid–structure interactions by complex formulations. To provide a broad overview on the scope and accuracy of different numerical linear models, in this paper, a comparative study based on the dynamic response assessment of cylindrical ground-supported containers under seismic excitation is conducted. The dynamic response in terms of liquid sloshing height, base shear force and overturning moment is analysed by means of: (a) a simplified mechanical model in which the behaviour of the liquid is represented by a discrete mass-spring system; (b) a complex model based on a Lagrangian fluid finite element approximation and (c) an experimental scaled model whose measured response is considered as benchmark. To obtain robust estimators of the structural response, three different types of cylindrical tanks, including broad and slender tanks, subjected to real ground acceleration time-histories are studied. The results indicate that the finite element model gives good approximation for all response parameters and the simplified mechanical model underestimate the sloshing height and overestimate base shear force and overturning moment.

This paper provides useful information about a passive method, usually applied on soils, for defining the frequencies of most infrastructures. Today, the eigen-frequency determination is one of the most significant and binding requirement aspects, especially in relation to the recent earthquakes in Italy (Accumoli, Norcia 2016; Finale Emilia 2012; L’Aquila 2009). The development of inexpensive, fast and reliable procedures to define the eigen-frequency of construction in general and of infrastructures in particular, is the aim of modern civil engineering. Currently, experimental tests are widely applied to evaluate the dynamic behavior of bridges. While the natural frequencies of a structure can be determined using different methods, passive methods are attractive because of their low costs and easy and fast procedures. In this paper, two passive methods, called standard spectral ratio (SSR) and horizontal to vertical spectral ratio (HVSR), are introduced and analyzed. The two methods are applied to estimate the frequencies in the transversal direction of a composite steel-concrete viaduct recently built in Italy. The comparison of the results obtained from SSR and HVSR and a finite element model confirms the possibility of applying the two methods for the dynamic characterization of bridges. In particular, the SSR method provides a correct estimation of the lower order natural frequencies and their degree of amplification. HVSR, which is typically used only on soil studies, provides a reliable early estimation of the frequency of a structure, if the latter is flexible, compared to the soil characteristics. The HVSR method is directly applied to the viaduct, so that an analogy is created between the soil layer and the structural elements. This paper is intended to show how the HVSR method typically applied to soil can reach good results in the dynamic characterization of Silea steel-concrete viaduct.

In a trapezoidal compound channel, the side slope of the main channel has a significant effect on the flow structure and the momentum exchange in the connecting region of the main channel and the floodplain. The three-dimensional compound channel flows with the 90°, 60°, 45° and 30° side slopes of main channel were simulated by solving the Navier–Stokes equations with the Reynolds Stress Model (RSM). The effects of main channel side slopes on the secondary currents, streamwise velocities, bed shear stresses, Reynolds shear stresses, turbulent intensities and the turbulence anisotropy were analyzed. The results show that (1) the secondary currents are modified as a result of the variation of the turbulence anisotropy (w′2¯−v′2¯), which is caused by the varied momentum exchange between the main channel and the floodplain; (2) as the main channel side slope decreases, the intensity of the secondary currents and their direct influence on the streamwise velocity, the bed shear stress, the Reynolds shear stress and the turbulent intensity becomes weaker. The deceleration of the streamwise velocity in the connecting region becomes less remarkable. The bed shear stresses tend to follow a more uniform distribution and are found to have one drop at the bottom of the main channel sidewall and the other drop at the edge of the floodplain when the side slope of the main channel is not vertical. These are different from the case of the vertical main channel side wall, in which only one minimum and one maximum values are observed at the interface region. The total magnitude of the turbulence intensity near the junction edge increases by a much smaller extent. The discharge ratio of the main channel increases while that of the floodplain decreases. The magnitude difference of −u ′ w ′ between the main channel and the floodplain in the interface region decreases, which implies the momentum transport becomes weaker due to the diminished secondary currents. These results will contribute for designing the most optimum cross-section shape for flood discharge of the compound channel.

Strain hardening cementitious composite (SHCC) is an attractive construction material for reinforced concrete (RC) structure strengthening, whereas the behavior of RC member with flexural strengthening using SHCC has not been clearly understood, since it is affected by various complex factors. In this paper, an experimental investigation into failure behavior of RC member with flexural strengthening using SHCC is implemented, which gives initial stage to the broad spectrum of the test. Moreover, a calculation model is also proposed for predicting the load-carrying capacity of flexural strengthened RC member using SHCC, in which the influence of varying SHCC layer thickness is considered. The results demonstrate the cracking behavior of SHCC layer is significantly affected by the varying SHCC layer thickness. The comparison of calculated and experimental results confirms the effectiveness of the proposed calculation model for predicting the load-carrying capacity of flexural strengthened RC member using SHCC.

The main objective of this present work is to estimate the seismic fragility of typical existing buildings in the north part of Algeria, in which we evaluate the performance, the seismic vulnerability and the damage of reinforced concrete frame structures and URM masonry buildings, existing in dominant way in the city of Algiers (Algeria). An analytical procedure for the derivation of fragility curves is proposed. The capacity spectrum method and seismic damage potential for the city, starting from capacity and fragility curves, are then discussed. Different tools regarding the determination of capacity curves of different existing structural systems by using a non-linear structural analysis are implemented and explained. Four damage states are defined for both structural systems. The earthquake action is expressed in terms of spectral values and the seismic quality of the buildings; the probabilities of the damage states are obtained considering a lognormal probability distribution. An ADRS format has been used for the studied area where a significant damage is obtained for mid-rise and high-rise masonry buildings.