Reinforced concrete Research Papers - Academia.edu (original) (raw)

Advances in wind pressure measurement and computer technology have made time-domain analyses of wind effects on high-rise structures possible in recent years. Time-domain solutions use aerodynamic and wind climatological databases and provide full phase information on wind-induced response that is lost in the frequency-domain approach; therefore, they can account rigorously for the superposed effects of any number of modes of vibration of any shape; for mode coupling; for wind directionality effects; and for the joint contributions of axial forces, bending moments, and shear forces in interaction equations used for structural design. Unlike the frequency-domain approach, in the time-domain approach, the process of determining wind effects and the structural design process, referred to jointly as database-assisted design (DAD), are integrated, transparent, and fully auditable. The objective of this study is to present the DAD approach as applied to highrise reinforced concrete (RC) buildings. Given the time histories of pressures, measured in the wind tunnel at a sufficient number of taps on the exterior faces of the building envelope for a sufficient number of mean speed directions and a preliminary design of the building, the structural engineer can calculate, as functions of wind speed and direction: (1) demand-to-capacity indexes for any number of members and cross sections, (2) interstory drift, (3) and top floor accelerations. These responses are properties of the structure independent of the wind climate, and constitute response databases used in conjunction with a wind climatological database to obtain the requisite wind effects for any specified mean recurrence interval. The design, which accounts for both wind and gravity effects, is performed iteratively until the design specifications are satisfied.

- by
- •
- Structural Engineering, Measurement, Reinforced concrete, Wind Pressure Coefficient

Application of Finite Element techniques of RC structures has been well established. However, this area still needs more research, because of the difficulty of modeling concrete in finite element analysis. Aim of this work is to develop a numerical approach based on the finite element formulation of three dimensional reinforced concrete beams. Concrete is modeled using twenty seven node brick lagrangian element. Bars and bond slip of the bar and concrete were modeled together by introducing the three dimensional truss-linkage elements. The validity of the model is established using comparison of the results with several wellknown tests from the literature.

- by Aeid Abdulrazeg
- •
- Materials Science, Finite Element, Multidisciplinary, Finite Element Analysis

Concrete in farm buildings is subjected to severe corrosion if manure is stored below slatted floors. Many chemicals associated with manure are identified as having a detrimental effect on concrete and the reinforcing steel embedded in the concrete. Of these, hydrogen sulfide is the most corrosive agent that leads to the rapid deterioration of concrete in barns. As well, manure has high concentrations of sulfates. In the present study, 48 concrete cylinders, 100 mm diameter and 100 mm high, were made with Portland cement, and various combinations of slag, fly ash and silica fume. Each has a reinforcing steel bar embedded in it. 24 cylinders are half immersed in sodium sulfate (20,000 ppm SO4 2- ) and also subjected to hydrogen sulfide gas (1,000 ppm H2S). The second set of 24 is subjected only to hydrogen sulfide gas. In each set, there are 8 different treatments. The specimens results indicate that after 16 cycles (each cycle is about five weeks long) of testing over 28 months, spe...

- by Vivian Abdelmseeh
- •
- Agricultural Engineering, Materials Science, Fly Ash, Agricultural

The opportunities provided by the use of Carbon Fiber Reinforced Polymer (CFRP) composites for the seismic repair of reinforced concrete (RC) structures were assessed on a full-scale dual system subjected to pseudodynamic tests in the... more

- by Gaetano Manfredi
- •
- Engineering, Civil Engineering, Structures and Fire Engineering, FRP

The purpose of this research is to evaluate and compare the relative merits of the two coating systems for reinforcing bars in concrete. A review is given of the nature and characteristics of both epoxy coated and galvanized steel for use as reinforcement in concrete. Also presented is an overview of the results from recent experimental work on the comparative corrosion behavior of uncoated black steel, epoxy coated steel, and galvanized steel in concrete.

- by Gokhan Gelisen
- •
- Bridge Engineering, Structural Designs in Bridges, Reinforcement, Epoxy

Story-high, prefabricated concrete façade elements with 6-8 cm thick outer layers were frequently used in building construction in the 1960/70s. In current construction and rehabilitation, they are much thicker (12-15 cm) or economically non-competitive, due to significantly increased concrete cover or the required use of stainless steel reinforcement, respectively, for durability. Additionally, these elements are placed further away from the support structure, owing to significantly increased requirement in thermal insulation. The outer shell of a façade element of the late 1960s was 4-8 cm away from the support structure while today, it is placed at a distance of 16-32 cm. The potential of replacing steel bars in prefabricated concrete façade elements by non-metallic glass-fiber reinforced polymer (GFRP) reinforcement was explored experimentally in a collaborative research project, targeting 5 cm thin elements and also requiring to test an associated new anchor system.

- by Hans-Rudolf Bärtschi
- •
- Engineering, Prefabrication, Conceptual Design, Polymer Composites

In recent decades, shear walls and tube structures have been the most appropriate structural forms for the construction of high-rise concrete buildings. Thus, recent Reinforced Concrete (RC) tall buildings have more complicated structural behaviour than before. Therefore, studying the structural systems and associated behaviour of these types of structures is very important. The main objective of this paper is to study the linear and nonlinear behaviour of one of the tallest RC buildings, a 56-storey structure, located in a high seismic zone in Iran. In this tower, shear wall systems with irregular openings are utilized under both gravity and lateral loads and may result in some especial issues in the behaviour of structural elements such as shear walls and coupling beams. The analytical methodologies and the results obtained in the evaluation of life-safety and collapse prevention of the building are also discussed. The weak zones of the structure based on the results are introduced, and a detailed discussion of some important structural aspects of the high-rise shear wall system with consideration of the concrete time dependency and constructional sequence effects is also included. Copyright © 2010 John Wiley & Sons, Ltd.

- by siamak epackachi
- •
- Civil Engineering, Nonlinear dynamics, Structural Design, Reinforced concrete

The earthquake of the 9th of July 1998 that hit in the central group of the Azores archipelago greatly affected the islands of Faial, Pico and São Jorge, reaching a magnitude of Mw 6.2 with the epicentre located about 15km northeast of the Faial Island. This earthquake allowed the collection of an unprecedented quantity of data concerning the characterisation of the building stock and the damage suffered by construction. This is the main purpose of this research, consisting essentially of three main aspects: (i) A detailed characterisation of the building stock, assigning a five category classification, from old traditional rubble stone masonry to reinforced concrete moment framed buildings; (ii) A detailed damage grade classification based on the different damage mechanisms observed; and, (iii) A seismic vulnerability assessment of the building stock. The results of the vulnerability assessment together with the building stock database and damage classification were integrated into a GIS tool, allowing the spatial visualation of damage scenarios, which is potentially useful for the planning of emergency response strategies and retrofitting priorities to mitigate and manage seismic risk.

- by Anibal Costa
- •
- Civil Engineering, Geology, Damage Mechanics, Emergency Response

The characterization and accurate determination of the chloride content in cement=concrete is very important for the assessment of the durability and safety of a concrete structure. The available analytical techniques are relatively expensive and time consuming. In this study, a laserinduced breakdown spectroscopy (LIBS) system was used for determination of elemental composition in three different types of cement samples. The plasma was generated by focusing a pulsed Nd: YAG laser at 1064 nm on the cement samples. The concentrations of different elements of significance for structural stability in cement samples were determined. The evaluation of the potential and the capabilities of LIBS as a rapid tool for characterization of cement samples is discussed. The optimum LIBS setup and experimental conditions to detect and measure chloride in building materials are reported. The LIBS results were compared with the results obtained using a standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP-ES). The limits of detection were determined, and calibration curves were measured. The results of this investigation indicate the reliability of LIBS to characterize different cement samples and to assess the chloride content in these cements.

- by Mohammed Alamoudi
- •
- Trace Metals, Structural Stability, Biological Sciences, Nondestructive testing

Modelling of existing reinforced concrete (r.c.) frames designed without specific seismic rules is a key problem for maintenance, structural upgrading and seismic assessment. In many European countries a very large percentage of reinforced concrete buildings are 40 years old, or even older; thus reinforcement consists of smooth rebars, since only in the 1970’s did early applications of deformed rebars appear. Technical literature on mechanical performances of anchored smooth rebars is non-comprehensive, mainly from the deformation standpoint, despite the relevance of this aspect to the response of critical regions, i.e. beam to column joints and column bases. In the present paper a series of experimental tests on smooth rebars are presented; they are aimed at describing in detail the force–slip relation for the bond mechanism for straight rebars and for anchoring end details, i.e. circular hooks with a 180∘ opening angle.

- by Giovanni Fabbrocino
- •
- Civil Engineering, Behavior, Structures and Fire Engineering, Anchoring

Secondary elements such as barriers, sidewalks, and diaphragms may increase the load carrying capacity of girder bridges. This in turn affects reliability. The objective of this study is to evaluate the potential benefit of secondary elements on the system reliability of girder bridges, if these elements are designed with the structural system to participate resisting vehicular live loads. Simple span,

- by Andrzej Nowak
- •
- Engineering, Civil Engineering, Finite element method, Finite Element

Reinforced concrete (RC) columns are often designed and assessed under the assumption that axial loads and bending moments are applied simultaneously and are perfectly correlated. Cases, however, may exist where loads are applied sequentially with varying degrees of correlation between them. This study lays the groundwork for the development of performance-based methods of assessment and design of RC columns under random loads. The effects of load path and load correlation are both taken into account. Section interaction diagrams are used as limit states to derive iso-reliability contours for RC columns under different load histories and correlations. Multiple column limit states are considered, including section-based and fiber-based limit states.

- by E. Spacone
- •
- Civil Engineering, Structures and Fire Engineering, Reinforced concrete

Results of electrochemical measurements of conductive coatings, based on the mixing of pigmentary graphite in a polymer matrix are presented in this work. Electrochemical parameters are determined for the investigated coatings during long-term anodic polarisation on reinforced concrete. Based on impedance measurements the electrochemical parameters of conducting coatings are calculated. It is shown that the investigated coatings can be used in cathodic protection of reinforced concrete. The investigations show that the optimum graphite contents in coatings used for protection of concrete should be in the range from 40% to 45%.

- by Kazimierz Darowicki
- •
- Civil Engineering, Materials Science, Cathodic Protection, Building

Timber-concrete structures can be applied to bridge superstructures of vicinal roads with innumerable advantages in relation to the usual structures made of timber or reinforced concrete. This paper presents both an experimental analysis and a theoretical study on models of bridges with timber and concrete composite structures whose systems of connections composed by nails or screws are semi-rigid. The experimental procedure consisted basically of bending tests in three panels, representing a bridge prototype to evaluate the performance structural. Besides this, in order to define the slip modulus shear tests in small specimens were performed. The theoretical study was based on differential equations developed from the equilibrium of forces and the compatibility of displacements and these results were compared to the Finite Element Method. From this analysis, it can be concluded that the timber-concrete composite structures have favorable perspective of application in this type of civil construction.

Although substantial advances have been achieved in last twenty years, in practice we are still far from taking full advantage of the potential of knowledge-based systems (KBS). Very few KBS have survived their evaluation period and only one third of those that were initially reported as successful are still in use. The primary purpose of the paper is to report on three KBS applications that have been developed for research purposes in the field of civil engineering. The main challenge underlying all three projects has been to develop computer support systems that would induce changes and improvements to the way that engineers solve their everyday problems. A great deal of effort has been put into eliciting knowledge and reasoning strategies from engineering experts with the aim of building up a computer model of their expertise in order to assist engineers in their decision-making processes. The paper closes by highlighting the principal achievements and the main issues concerning the future development of KBS for solving real life problems.

- by cris domingues
- •
- Engineering, Software Engineering, Knowledge Based System, Computer Model

The electrochemical behaviour of reinforcing steel in plain and blended cement concrete specimens placed in sulphate, chloride and sulphate-chloride environments was investigated. The effect of cement composition and the exposure condition on the corrosion behaviour of reinforcing steel was evaluated by measuring corrosion potentials at periodic intervals and conducting potentio-dynamic scans after two and half years of exposure. The corrosion potential data indicated passive corrosion in plain and blended cement concrete specimens placed in the pure sulphate environment. The time to initiation of reinforcement corrosion, however, was higher in blended cements than plain cements in all chloride and chloride-sulphate environments. The concomitant presence of suphate and chloride salts did not significantly influence the time to corrosion initiation. The corrosion rate, however, was significantly influenced by the quantum of sulphate ions associated with the chloride salts. The superior performance of silica fume blended cement, in terms of longer time to corrosion initiation and lower corrosion rate, indicates its potential in enhancing the useful service life of reinforced concrete structures placed in the chloride-sulphate environments.

Fiber reinforced polymer (FRP) materials are continuing to show great promise for use in strengthening reinforced concrete (RC) structures. These materials are an excellent option for use as external reinforcing because of their light weight, resistance to corrosion, and high strength. Externally bonded FRP sheets have been used to increase moment capacity of flexural members and to improve confinement in compression members.

A significant number of existing reinforced-concrete bridges all over the world require maintenance and repair. Hence, the need for a rapid evaluation procedure for the diagnosis of existing bridges. This paper presents the application of a dynamic analysis methodology for structural evaluation of reinforced-concrete bridges. The methodology is based on the application of ambient vibrations non-destructive testing method and the identification of the structure total response using finite element method. A case study of a three span reinforced concrete bridge in a strong seismic activity area in the north of Algeria is analysed. The ambient vibration testing was carried out on the bridge, before and after its repair by the application of carbon fibre composites. The tests were conducted using an acquisition system made up of four accelerometers with three components placed at specific locations on the bridge. The finite element model gave comparable results to the experimental ambient vibrations tests. The modal parameters of the bridge before and after repair were identified by this in situ testing. The application of composite material to strengthen the structure increases the transverse rigidity of the structure and thus its modal frequency.

- by Mourad Abdessemed
- •
- Civil Engineering, Finite element method, Numerical Modelling, Finite Element

Two, full size, reinforced concrete frames were put on a shaking table and underwent seismic excitations with increasing intensities. The aim of the reported experiment was to study changes in their dynamic, modal parameters due to development of cracks in concrete. Dynamic identification of these frames was carried out through diagnostic tests interlaced with the damaging excitations. This paper presents the results of their identification in various states of damage, using low level non-destructive damage estimation methods. A characteristic decrease of natural frequencies and an increase of structural damping was observed. The drop of the natural frequency was fastest for the 1st mode and slower for the further modes. It was noted that the loss of natural frequencies equaled about 10% and still the first cracks could not be visually detected (loss of stiffness 15%). The advantages and disadvantages of the application of a shaking table for modal analyses of full size, civil engineering structures are pointed out in detail.

This paper investigated two-way concrete slabs reinforced with steel bars milled from scrap metals. The slabs were simply supported on all four sides and tested under a central concentrated load. The average experimental failure loads for monotonic and cyclic loading were 32.8kN and 26.7kN, respectively. In addition, the experimental failure loads averaged 127% and 98% of the theoretical punching shear strength of the two-way reinforced concrete section under monotonic and cyclic loads, respectively. Collapse of the slabs always occurred through a combination of the crushing of the concrete after flexural cracks propagated extensively, and punching shear. Finally, a recommendation based on the analysis of the results for the design of two-way slabs using steel bars milled from scrap metals is proposed.

- by Mark Adom-Asamoah
- •
- Crack propagation, Developing Country, Materials Design, Cyclic Loading
- by Bibiana Maria Luccioni
- •
- Civil Engineering, Structural Engineering, Stress, Reinforced concrete

Стаття присвячена методиці розрахунку стиснутих залізобетонних елементів на основі деформаційної моделі за національними нормами з урахуванням впливів першого і другого порядку. Наведено алгоритм розрахунку стиснутих елементів за другою... more

- by Olha Uzhehova
- •
- Deformation and strain, Reinforced concrete
- by Murat Dicleli
- •
- Civil Engineering, Earthquake Engineering, Energy, Stress

This paper deals with strengthening of RC (reinforced concrete) two-way slabs with CFRP (carbon fibre reinforced plastic) strips bonded to the tensile face. The first part describes a FEM (finite element) development. A 2-D finite element for orthotropic composite plates is used to describe elastic behaviour of RC slabs strengthened with CFRP strips. In the second part an experimental investigation is conducted on RC two-way slabs strengthened with CFRP. Finally the experimental results are compared to the numerical predictions.

Early and accurate detection, location and assessment of damage in reinforced concrete bridge decks may be beneficial in the scheduling and performance of maintenance and rehabilitation activities. This article presents the results of a multiple sensor study of the condition of the reinforced concrete deck of the Van Buren Road Bridge in Dumfries, VA. The tests compared the following five different methods: (1) visual inspection and photographic recording; (2) half-cell electrochemical potential; (3) impulse type multipoint scanning ground penetrating radar; (4) chain drag and (5) impact echo. The bridge was tested on two separate occasions. The results of the tests were that each instrument nominally performed and collected data as expected, but that the condition assessments did not necessarily agree. The data are registered, overlaid and compared. The potential for developing automated multisensor systems that fuse data for efficient and effective bridge deck measurements is discussed.

- by Dylan Burns and +1
- •
- Civil Engineering, Ground Penetrating Radar, Ultrasound, Reinforced concrete

An unusually large number of minarets, which are slender tower structures, collapsed during the 1999 Kocaeli and Duzce, Turkey earthquakes with resulting damage to surrounding buildings and loss of life. The potential effects of the subsequently observed poor reinforcement detailing on the dynamic response is discussed. The probable cause of the extensive damage to reinforced concrete minarets is investigated by studying the observed failure modes and their seismic performance, and through the dynamic analysis of a representative minaret. The effects of spiral stairs, door openings, and balconies on the dynamic behavior are examined. The maximum dynamic internal force demands were compared with the calculated capacities. The locations of the maximum axial, shear, and flexural demands predicted from the finite element analysis of the minaret model were consistent with the earthquake damage observed at those critical locations.

- by Julian Alcala
- •
- Civil Engineering, Heuristics, Simulated Annealing, Optimization techniques

Steel bracing systems can be used effectively for seismic retrofitting of existing RC buildings as well as for seismic design of new buildings. Although adaptation of bracing to upgrade the lateral load capacity of existing RC frames has been the subject of a number of successful studies, guidelines for its use in newly constructed RC frames need to be further developed. An important consideration in the design of steel-braced RC frames is the level of interaction between the strength capacities of the RC frame and the bracing system. In this paper, results of experimental and numerical investigations aimed at evaluating the level of capacity interaction between the two systems are discussed. For these investigations, cyclic loading tests are conducted on scaled moment resisting frames with and without bracing. It is found that the capacity interaction is primarily due to the connections overstrength. The experimental results are also used to calibrate full-scale numerical models. A parametric numerical investigation on the effects of the main problem variables is then conducted and the influence of each parameter on the level of the overstrength is determined. Based on these findings, guidelines for the seismic design of the internally cross-braced RC frames with direct connections are provided.

Deterioration of reinforced concrete and the reliability of deteriorating structures have been, and still are, widely researched fields. A critical aspect of this research effort is the integration of deterioration modelling with reliability assessment. This paper focuses on this issue and illustrates how the integration of these techniques can lead towards more realistic predictions of the time dependent performance of reinforced concrete bridge structures. The introduction of spatial random fields into the proposed approach facilitates the identification of the type and quantity of data required to update models and improve predictions. This is an essential step in the rational prioritisation of maintenance actions for such structures. However, there are still important gaps both in understanding and modelling the deterioration process, as well as in assessing its influence on bridge performance. In this respect, the methodology presented in the paper can be developed further, and...

- by Marios Chryssanthopoulos
- •
- Reliability, Spatial Variability, Bridges, Reinforced concrete

Current distribution from a surface mounted anode to steel reinforcement in atmospherically exposed concrete is modelled as a function of the condition of the steel, the resistivity of the concrete and anode-steel geometry. The boundary conditions at the steel have a significant effect on current distribution with more uniform distribution arising at low steel corrosion rates. In a typical situation the surface of a steel bar facing the anode may receive 50% more current than the opposite surface. As cathodic protection has proved to be effective in these cases, a basis for many design decisions that influence current distribution is that their effect is small by comparison. When more than one layer of reinforcement is present the current distribution is significantly worse. In this case a surface anode may not be enough and discrete anodes may be necessary to improve current distribution. An increase in the concrete resistivity, cover and the anode to cathode area ratio at a constant anode current density will increase the voltage drop through the concrete inducing an improvement in the environment at the steel that promotes steel passivity. Ó

- by Nick Buenfeld
- •
- Civil Engineering, Cathodic Protection, Building, Current Density
- by Frank Foulkes
- •
- Civil Engineering, Building, Iron, Reinforced concrete

The procedures to do response analysis of a seismically isolated building are summarized based on

- by Demin Feng and +1
- •
- Structural Engineering, Base Isolation, Building Codes, Reinforced concrete

Much effort has been made in recent years to adopt suitable strategies for durability design of concrete. Most of this work has focused on the development of 'performance specifications' for concrete. However, there are many barriers and limitations to successful implementation of these strategies for early-age control of reinforced concrete durability. This article reviews some of the recent efforts in the implementation of such strategies. It describes the South African approach to durability design, which is based on performance specifications that are to be satisfied at the time of construction. Case studies are presented on approaches to reinforced concrete design and the corresponding application of a durability performance specification, to highlight the potential for adopting a probabilitybased methodology for durability design. Finally, the paper attempts to provide a way forward towards successful utilization of such approaches, with particular emphasis on the construction industry in India.

- by Mark Alexander
- •
- Construction Industry, Case Study, South African, Reinforced concrete

Computers are an integral part of day to day activities in engineering design and engineers have utilised various applications to assist them improve their design. Although computers are used to model a variety of engineering activities, currently the main focus of computer applications are areas with well defined rules. Activities related to the conceptual stage of the design process are generally untouched by computers.Artificial neural networks (ANN) have recently been widely used to model some of the human activities in many areas of science and engineering. Early applications of NN in civil engineering occurred the late eighties. One of the distinct characteristics of the ANN is its ability to learn from experience and examples and then to adapt with changing situations. Engineers often deal with incomplete and noisy data, which is one area where NN are most applicable. This is particularly the case at the conceptual stage of the design process.This paper presents practical guidelines for designing ANN for engineering applications.A brief introduction to NN is given; major aspects of three types of NN, multi-layer perceptron (MLP), radial basis network (RBF) and normalised RBF (NRBF) are discussed; new methods for selection and normalisation of training data are introduced and a practical example of a reinforced concrete slab design is presented.

- by SUMIT BHATI
- •
- Engineering, Engineering Design, Neural Network, Design process

This paper reports on the experimental assessment of the punching shear behaviour of reinforced recycled concrete slabs characterized by fine natural aggregates and coarse recycled aggregates. In particular, the latter were obtained only from demolished concrete. The experimental campaign has been carried out on 12 specimens. Moreover, three reinforced natural aggregate concrete slabs have been casted and tested as benchmarks. Four replacement percentages (30, 50, 80 and 100%) of coarse recycled aggregates in place of coarse natural aggregates have been considered. The punching shear behaviour of simply supported reinforced recycled concrete slabs under a central patch load has been investigated by means of failure patterns, ultimate loads and deflection–load curves.
Moreover, comparisons and a review of international code models for slabs under punching shear have been developed. The results show a reduction in recycled concrete mechanical performance with increasing replacement percentage of natural aggregate with coarse recycled aggregates. However, the reduced recycled concrete performance does not translate directly to the punching shear strength of reinforced recycled concrete slabs; indeed, the punching forces of all recycled concrete slabs tested are very similar to those of slabs realized with ordinary reinforced concrete. Actually, although the theoretical models on the punching shear are based on the characteristics of the concrete, this study indicates that the reinforcement role is of paramount relevance.

- by Lorena Francesconi and +1
- •
- Civil Engineering, Structural Engineering, Recycled Construction Materials, Concrete Technology

This paper presents a novel analytical formulation of an element removal algorithm based on dynamic equilibrium and the resulting transient change in system kinematics, by applying imposed accelerations instead of external forces at a node where an element was once connected. The algorithm is implemented into an open-source finite element code, numerically tested using a benchmark structural system with simplified element removal criteria, and able to capture the effect of uncertainty in member capacity. Realistic element removal criteria are introduced for mode-dependent gravity load collapse of seismically deficient and retrofitted reinforced concrete (RC) columns and unreinforced masonry (URM) infill walls. Two applications are conducted using structural systems of RC frames with URM infill walls. The first is a probabilistic study of a one-story model subjected to an ensemble of 14 ground motion recordings from similar neighboring sites during an earthquake event. The study produces empirical probability curves for partial and complete collapse conditioned on different hazard levels, and concludes that the intra-event variability is a major source of uncertainty affecting the outcome of progressive collapse simulations. The second application is a deterministic sensitivity study of progressive collapse response in a five-story structural model to uncertainty in live load, stiffness, damping, and seismic hazard level, subjected to one ground motion record. The analysis identifies the time at incipient collapse as an adequate sensitivity measure, and the uncertainty in ground motion intensity as the most important, followed by the stiffness of the URM infill wall. Copyright © 2009 John Wiley & Sons, Ltd.

- by Mohamed Talaat
- •
- Civil Engineering, Algorithms, Earthquake Engineering, Finite Element

It is desirable to verify the structural performance based on a multi-hazard approach, taking into account the critical actions the structure in question could be subjected to during its lifetime. This study presents a proposal for a probabilistic model for multi-hazard risk associated with the limit state of collapse for a reinforced concrete (RC) structure subjected to blast threats in the presence of seismic risk. The annual risk of structural collapse is calculated taking into account both the collapse caused by an earthquake event and the blast-induced progressive collapse. The blast fragility is calculated using a simulation procedure for generating possible blast configurations, and verifying the structural stability under gravity loading of the damaged structure, using a kinematic plastic limit analysis. As a case study, the blast and seismic fragilities of a generic four-storey RC building located in seismic zone are calculated and implemented in the framework of a multi-hazard procedure, leading to the evaluation of the annual risk of collapse.

- by Gaetano Manfredi
- •
- Civil Engineering, Monte Carlo Simulation, Risk assessment, Structural Stability

This paper describes recently-completed research at the University of Bath within the BRE Centre of Innovative Construction Materials in the field of fibre-reinforced polymer (FRP) materials for use in concrete structures. The research described has been carried out in collaboration with Parsons Brinckerhoff, Bristol. The use of FRP to strengthen concrete structures is a mainstream technology throughout the world, and specific research projects aimed at better understanding the underlying mechanics of this technique are described here. Further, the use of FRP to internally reinforce concrete structures is described in the context of effective use of all materials, coupled with the assurance of ductile behaviour.

Most codes of practice, like ACI 318-14, 9.9.1.3, require the use of strut-and-tie modeling (STM) to deal with reinforced concrete continuous deep beams (rc-cdbs). Though, investigations that conducted on rc-cdbs did not include all the most influential parameters. This work presents an analytical parametric study using STM stated by ACI 318-14 to calculate load capacity of 20 rc-cdbs with different parameters. The parameters took into consideration in the current work are shear span to overall depth ratio (a/h), width of beam (bw), width of bearing plate (BP), concrete compressive strength (f'c) and amount of vertical shear web reinforcement (pv). It is seen that the load capacity decreases by about 14% to 37% when a/h increases by about 33% to 100%. It is also seen that load capacity increases by about 33% to 100% when bw increases by about 33% to 100%, while the load capacity increases by about 10% to 30% when BP increases by about 33% to 100%. Finally, it is found that load capacity increases by about 35% to 100% when compressive strength increases by about 35% to 100%, while the load capacity increases by about 0% to 25% when pv increases by about 33% to 100%.

- by Khattab S Abdul-Razzaq and +1
- •
- Reinforced concrete

Reinforced concrete poles are very popular in transmission lines due to their economic efficiency. However, these poles have structural safety issues in their service terms that are caused by cracks, corrosion, deterioration, and short-circuiting of internal reinforcing steel wires. Therefore, they must be periodically inspected to evaluate their structural safety. There are many methods of performing external inspection after installation at an actual site. However, on-site nondestructive safety inspection of steel reinforcement wires inside poles is very difficult. In this study, we developed an application that classifies the magnetic field signals of multiple channels, as measured from the actual poles. Initially, the signal data were gathered by inserting sensors into the poles, and these data were then used to learn the patterns of safe and damaged features. These features were then processed with the isometric feature mapping (ISOMAP) dimensionality reduction algorithm. Subsequently, the resulting reduced data were processed with a random forest classification algorithm. The proposed method could elucidate whether the internal wires of the poles were broken or not according to actual sensor data. This method can be applied for evaluating the structural integrity of concrete poles in combination with portable devices for signal measurement (under development).

Purpose -This work seeks to present a systematic study that aimed to provide quantitative understanding of the fundamental factors that influence the chloride threshold of pitting corrosion of steel in concrete, by conducting a set of laboratory tests to assess the corrosion potential (E corr ) and pitting potential (E pit ) of steel coupons in simulated concrete pore solutions. Design/methodology/approach -With the aid of artificial neural network, the laboratory data were used to establish a phenomenological model correlating the influential factors (total chloride concentration, chloride binding, solution pH, and dissolved oxygen (DO) concentration) with the pitting risk (characterized by E corr 2 E pit ). Three-dimensional response surfaces were then constructed to illustrate such predicted correlations and to shed light on the complex interactions between various influential factors. Findings -The results indicate that the threshold [Cl 2 ]/[OH 2 ] of steel rebar in simulated concrete pore solutions is a function of DO concentration, pH and chloride binding, instead of a unique value. Research limitations/implications -The limitations and implications of the research findings were also discussed. Practical implications -This research could have significant practical implications in predicting the service life of new or existing reinforced concrete in chloride-laden environments. Originality/value -This study further advances the knowledge base relevant to the chloride-induced corrosion of steel rebar in concrete.

- by tuan anh Nguyen
- •
- Materials Engineering, Corrosion, Design Methodology, Knowledge base

Muchos edificios de concreto dañados por los sismos ocurridos en 1985 en la ciudad de México han sido reforzados colocando camisas de acero en sus columnas, que consisten de ángulos a lo largo de las aristas y placas o soleras transversales, sin que se tenga evidencia experimental del comportamiento de las columnas así reforzadas. Con base en lo anterior, se han realizado tres series de ensayes en columnas de concreto reforzadas con camisas de acero sujetas a carga axial y carga transversal alternante. El objetivo fue determinar si su comportamiento era adecuado y si su resistencia a fuerza cortante se podía calcular con los procedimientos usuales. Las variables estudiadas fueron el tamaño de los ángulos y las placas transversales que constituían la camisa, el daño previo a las columnas y distintos procedimientos constructivos: uso de resina epóxica para pegar los ángulos al concreto, sujetarlos a presión antes de soldar las soleras, soldar las soleras sin pegar ni presionar los ángulos, calentar las soleras y soldarlas antes de que se enfríen y combinaciones de estos procedimientos. Se describe el trabajo experimental y se presentan estudios analíticos para la interpretación de los ensayes.

- by Oscar Gonzalez
- •
- Physics, Mexico City, Reinforced concrete

From the early 20th-century the gradual transformation of the theory and constructive techniques led from the masonry buildings predominance to the reinforced concrete's (RC) structures. Together with structures conceived with a definite role for the earthquake behaviour, the spreading of RC technology caused the birth of mixed solutions starting from existing structures in order to satisfy functional aspects: masonry structures subjected to internal demolishment, column insertions, RC staircases insertions, plan enlargements or raisings-up by mean of concrete structures. The structural variety is quite wide and the complex set of specific cases eludes the coded schemes: therefore subject of particular interest becomes the vulnerability of this class. Moreover, although there is a well-established background focused on the non linear analysis of masonry structures and RC frames, the set of numerical and experimental instruments for the study of the interaction effects is limited. In this paper, in the masonry's idealisation as equivalent 3D frame , a formulation and implementation of non linear elements is proposed in order to model RC columns, beams and walls. The adopted approach idealises the behaviour as elasto-perfectly plastic with limited resistance and plasticity concentrated at the endelement; the considered failure's mechanisms are as follows: shear and axial stress as brittle failure and axial-bending as ductile failure. Some examples show the efficiency of this method and highlight the behaviour's peculiarity of these structures.

Addressing the use of reinforced concrete for restoration at archaeological sites, Paola Pesaresi, the conservation architect with the Herculaneum Conservation Project, reviews how concrete was employed at Herculaneum during the first half of the twentieth century, and how the subsequent deterioration of the concrete elements incorporated into the site is now being handled by authorities there.

A simplified procedure to estimate drift based on the area of loadresisting elements is presented and its results are compared with those of the equivalent-period method and the target-displacement method as defined in FEMA-273 (1997). All three methods are used to estimate the upper-bound drift based on simple parameters that represent the lateral stiffness and mass of a structure. The accuracy of the methods was evaluated using experimental results from 152 earthquake simulator tests found in the literature. Coefficients of variation for the measured-to-calculated drift ratios ranged between 0.6 and 0.75, indicating that the accuracy of the drift estimates afforded by the three methods was similar for the set of test results evaluated. Additional comparisons are presented for the proposed method based on 720 nonlinear analyses of notional frames and the measured response of an instrumented building.

- by Adolfo Matamoros
- •
- Civil Engineering, Reinforced concrete

Reinforced concrete (RC) columns in buildings often need strengthening either due to defects in the columns themselves, having to support higher loads than those foreseen in the initial design of the structure, or as the result of ageing or accidental damage. The use of steel caging for this purpose is now a common practice in many countries throughout the world. Based on the results of an experimental study, this paper presents a parametric study using finite element models carried out with the aim of analysing the behaviour of RC columns strengthened by steel caging. The results of the study are used to analyse the influence that various parameters have on the behaviour of the strengthened column (size of the angles, the yield stress of the steel of the cage, the compressive strength of the concrete in the column, the size of the strips, the addition of an extra strip at the ends of the cage, the friction coefficient between the layer of mortar and the steel of the cage). The results obtained from the parametric study allow a series of guidelines to be established.

A new method is described for thein-situ measurement of electrical resistivity of concrete structures. The method is based on the early work of J. Newman who calculated the electrolyte resistivity between a disk and a counter electrode located at infinity. This method has the advantage compared with Wenner's of using a single small electrode for the measurements. In this paper, results are presented comparing this method with Wenner's and with results carried out using a conductivity cell in electrolytes. Finally, values of resistivity are compared to corrosion intensity, and a threshold for active corrosion is suggested. On décrit une nouvelle méthode de mesure de la résistivité électrique du béton dont la technique est basée sur un travail ancien de J. Newman qui avait calculé la résistivité entre un disque et une électrode auxiliaire placée à l'infini. Comparée à la méthode de Wenner, cette méthode présente l'avantage de n'utiliser, pour les mesures, qu'une petite électrode. Dans cet article, on présente les résultats de la comparaison établie avec la méthode de Wenner et avec les résultats obtenus avec une cellule de conductivité placée dans les électrolytes. Enfin, on compare les valeurs de la résistivité du béton avec celles de l'intensité de la corrosion et on suggère un seuil de corrosion active.