On the robustness to corrosion in the life cycle assessment of an existing reinforced concrete bridge

Management of existing structures has traditionally been based on condition assessment, based on visual inspections, disregarding the susceptibility of different structural types to aging and deterioration. Robustness, as a measure of the effects of unpredictable damage to structural safety can be a complementary information to the results of inspection. Although robustness has mostly been used to evaluate the consequences of extreme events, a similar framework can be used to investigate the result of aging, allowing a better understanding of the potential effects of deterioration and allowing a better allocation of available maintenance funding. In this work, a probabilistic structural robustness indicator is used to quantify the susceptibility of structures to corrosion. The methodology is exemplified through a case study comprising an existing reinforced concrete bridge deck, heavily damaged due to reinforcement corrosion, and finally demolished due to safety concerns. Robustness measures the bridge deck safety tolerance to reinforcement corrosion. The principal effects of corrosion, including loss of area and bond between concrete and steel are modelled using a non-linear finite-element model, coupled with a Response Surface Method to compute the bridge reliability as a function of the corrosion level, and finally used to assess robustness. Results show that the redundancy of the bridge allows significant redistribution of loads between elements with different corrosion levels. As a result, the bridge presents significant robustness and tolerance to reinforcement corrosion.     

混凝土企业如何面对市场的竞争

面对建筑市场激烈的竞争,采取压价竞争是有意无意的恶性竞争,恶性压价竞争实际上是饮鸩止渴。正确的竞争路线是创品牌,保证质量。建筑工程各环节同时是产品,又是用户。因此,需要合作方式提高质量,以质量去赢得市场,这才是双赢的道路。     

Buckling of elastically restrained steel columns under longitudinal non-uniform temperature distribution

Columns under natural fire conditions are usually exposed to a non-uniform temperature distribution in the longitudinal direction. The motivation for this study stems from zone modeling of a compartment fire where the gas layers are artificially divided into two zones, namely the hotter upper zone and the cooler lower zone. However, for field modeling of a compartment fire, more detailed information of the temperature distribution can be obtained. Depending on the required accuracy, two different idealizations of temperature distributions are analyzed in this paper, namely linear distribution from zone modeling and piece-wise step distribution from field modeling in the longitudinal direction. Compared to a column with uniform temperature distribution, both of them represent more realistically the thermal response of a column, which experiences greater temperature with increasing height. The difference in temperature between the top and bottom ends of a column can be quite significant, particularly prior to the flashover condition. Advantage can be made of this in a performance-based approach to ascertain the stability of a column subjected to a prescribed fire size. In this paper, the stability of a pin-ended steel column under a non-uniform temperature distribution is studied. Although the formulations are based on linear elastic assumptions, the paper explores the validity aspect of the approach and shows that it can be applied to columns with a minimum slenderness ratio where plasticity is negligible. Across a section, the temperature is assumed to be uniform. Two linear elastic springs connected to the column ends simulate the axial restraints from the adjoining unheated structure. The objective is to derive closed-form solutions to enable engineers to quickly ascertain the column stability under a non-uniform temperature distribution, without recourse to finite element modeling.     

Management of bridges with shallow foundations exposed to local scour

Abstract

The Serbian road network includes a large portion of bridges with shallow foundations vulnerable to local scour as tragically demonstrated during the extreme flooding in May 2014. Currently, the bridge management procedures in Serbia and worldwide do not comprehensively account for a risk of bridge failure due to flooding and fail to provide sufficient information for the decision-making. Thus, a novel methodology for quantitative vulnerability assessment is suggested as a tool to identify the most vulnerable bridges in a network. Herein, the essential task is evaluation of the conditional probability of a bridge failure due to local scour in a flooding event of a certain magnitude. To apply this approach on a network level, there is a dire need to establish precise practice-ready guidelines on an optimal set of information to be used and/or collected in situ, which is discussed on an example of the Serbian bridge database. The vulnerability of a bridge to local scour may be used as a comprehensive indicator of a bridge performance in a flooding event. For a network level, the vulnerability maps with respect to flooding of different magnitudes will give road operators crucial information to apply adequate quality control plans to vulnerable bridges.     

New approach to determine the plastic viscosity of self-compacting concrete

The rheology of concrete is best measured with the use of a rheometer. The slump flow test gives a good indication of the flowability of the mixture and is therefore still used extensively to judge the workability of SCC mixtures. However, this test presents some defects. The objective of this paper is to develop a new methodology for measuring the workability of a SCC.In this article, we have proposed a correlation between the plastic viscosity of concrete, the time and the characteristics of the flow final profile from the V-funnel coupled to a Plexiglas horizontal channel. The proposed approach, verified by experimental results, represents a simple, economical and usable tool on building site, and it allows to characterize rheologically the SCC from its flow.The comparison between our approach and the experimental values of the plastic viscosity shows that, in a laboratory or on site, instead of using a rheometer we can use our approach to characterize the rheological behavior of a SCC.     

CFD-DEM modeling of geotextile clogging in tunnel drainage systems

In this study, a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) method we used to investigate the hydraulic deterioration of a geotextile due to clogging in tunnel drainage systems. Initially, a framework was developed to generate and test a numerical representation of a typical non-woven geotextile. Following model validation, we carried out parametric analysis to examine the effect of fine content, crack angle, and groundwater inflow. The results showed a general trend of pressure increase associated with increasing both the crack angle and fine content. This increase was found to decay at larger crack angles and high content of fines. Interestingly, increasing groundwater inflow was found to had minimal effect on the final deposition of the clogging particles. Finally, an approximate semi-analytical model was developed to describe the pressure increase due to clogging. The model was able to provide a good match with the data obtained from the numerical analysis.     

From file to factory: Innovative design solutions for multi-storey timber buildings applied to project Zembla in Kalmar,Sweden

A “file-to-factory” process of computer technology is a way to both maximise efficiency throughout the building process, increase a building's performance, and be able to add interesting architectural possibilities throughout the design phase. The authors investigate a novel approach that produces a set of building trajectories rather than a set of buildings, yet yields a series of build-able examples of those trajectories. This paper evaluates how this series of stacked multi-storey timber buildings can be both incorporated within a file-to-factory process, and give rise to creating new innovative solutions throughout the entire design and manufacturing process. This process is applied to a real Swedish project called Zembla. It redefines the notion of sprawl, turning it into a progressive tactics for linking the city fabric to rural areas. It is a post-sustainable file-to-factory-produced timber ground-scraper; soaring above ground and water, suggesting a new way of making city-sized buildings for the future. A plug-in grid-shell structure is designed to contain a minimal amount of timber elements, beams make up the lattice, cross-laminated panels add structural support, surfaces come together to form the living capsules. Having the structure undulate across the topography and touching the ground in as few places as possible uses the dichotomy between landscape and urbanism, bringing the city to the people living in less densified areas. Each living unit is customised to its topological conditions within the grid.     

LRFD for assessment of deteriorating existing structures

The deterioration of infrastructures is a widespread problem in many countries. In order to assess such structures for continued future service, simple and practical tools need to be developed for evaluating the time-dependent reliability and performance of the structures. This paper describes the concept of a resistance reduction factor due to degradation of a component to approximate a time-dependent reliability problem as a time-independent one. With the factor the time-varying resistance can be equivalently replaced with a time-invariant resistance, and load and resistance factors can be determined for the assessment applying simple AFOSM. An approximation method to determine the factor is proposed, and a numerical example shows that the target reliability level can be achieved fairly accurately using an approximate reduction factor. It is also demonstrated that the approximation method can be applied to estimate a resistance reduction factor including the cases when the strength of a component is restored to some extent by means of inspection and repair, and, accordingly, to evaluate the effect of inspection and repair on the reliability of the component.     

六奉公路大治河桥系杆悬吊模板施工技术

位于上海市六奉公路上的大治河桥,为主跨120m的下承式钢管混凝土拱桥,其桥拱的安装采用“先拱后梁”的施工工艺。系杆的施工依托于劲性骨架和吊杆作为承重构件,采用悬吊模板进行施工。本文通过该桥系杆悬吊模板施工实例,介绍系杆悬吊模板实现无支架现浇施工的施工工艺及其技术要点。     

Seismic functional reliability analysis of water distribution networks

Due to the huge destructive power of strong earthquakes, many breaks appear on water pipelines after such events. As a result, water leaks from these breaks, causing function loss of water distribution networks (WDNs). In order to evaluate the seismic performance of WDNs, these leaks cannot be ignored. In this paper, by adding a leakage model to the hydraulic equation of WDNs in a daily operation state, a new hydraulic equation is established to describe WDNs after the occurrence of earthquakes. As it is a stochastic equation, a random perturbation method is used to solve the equation and give the mean, standard deviation and skewness of the nodal head. In the meantime, a performance function is established to evaluate the reliability of WDNs. Three reliability analysis methods, a mean first-order second-moment method and two third-moment methods, are used to give the seismic functional reliability of WDNs. Meanwhile, two networks, a small WDN and an actual WDN which suffered serious damages during the Wenchuan Earthquake, 2008, are studied to compare the efficiency and precision of the three reliability methods.