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Past lateral cyclic or seismic tests of concrete frames with smooth bars in columns are very few and limited as far as the test structure's size and geometry are concerned; moreover, they have not focused on the effect of detailing and lap-splicing of such bars on local and global behaviour. To help fill this knowledge gap with new data, the paper presents the cyclic lateral load test of a 2:3-scale three-storey, one-by-two-bay, strong beam-weak column RC frame, focusing on the effects of the column's smooth bars and of their detailing on local and global behaviour. Slippage of bars caused concentration of column deformations in flexural cracks at the top and base sections and gave to the global hysteresis loops a shape typical of bond-slip behaviour, but without cyclic strength decay. Despite chord rotation demands of up to 0.055 rads and storey drifts of almost 5%, damage was limited and had nothing to do with the use of smooth bars in the columns. Despite the important role of bar slippage for the response, bar strains show that wherever the surrounding concrete was in compression, column bars were in compression as well. Lap splices at and/or FRP wrapping of column end regions did not have systematic effects on column behaviour. Overall, no adverse effect of the use of smooth bars was identified. [ABSTRACT FROM AUTHOR]

The island of Hispaniola, shared by the Dominican Republic and Haiti, is located in a subduction zone between the North America plate and the Caribbean plate. In addition, there are 13 geological faults in the interior of the island, some of which have shown the potential to generate earthquakes of magnitude 7.5 and higher. Thus, the whole island is considered to be a high seismic risk region. In the past 100 years, several earthquakes have affected both parts of the island. In the case of the Dominican Republic, two earthquakes stand out: a magnitude 8.1 earthquake on August 4, 1946, north of the Samaná Province, which caused a tsunami, soil liquefaction, and the loss of about 100 lives, and a magnitude 6.5 earthquake on September 22, 2003, in the city of Puerto Plata, which caused significant damage for infrastructures. Among the observed effects, the partial and total collapse of several school buildings had a remarkable impact on local communities. In addition to the high seismic risk, a large part of the national infrastructure may exhibit high vulnerability to earthquakes because the seismic regulations had been the same for 32 years, namely from 1979 to 2011. During these three decades, thousands of structures were built nationwide, including essential facilities such as hospitals and schools. Considering that the current student population in public schools in the Dominican Republic is over 2 million, with the majority attending buildings that were designed with the 1979 seismic code and which proved to be highly vulnerable during the Puerto Plata earthquake, it is vital to take measures that reduce the risk and minimize potential earthquake damage to school buildings. In this context, the Technological Institute of Santo Domingo (INTEC) has undertaken recently a project with the main objective to assess the seismic vulnerability of 22 schools located in the San Cristóbal Province, in the south of the Dominican Republic. The latter schools were all built prior to the adoption of the current updated seismic code. This paper presents the results of the assessment of the Fernando Cabral Ortega School. Although only the results of a single RC building are presented, the response of such structure can be considered representative of a portfolio of existing schools in Dominican Republic. [ABSTRACT FROM AUTHOR]

Structural elements in old reinforced concrete (RC) frame buildings are often prone to shear or flexure-shear failure, which can eventually lead to loss of axial load capacity of vertical elements and initiate vertical progressive collapse of a building. An experimental investigation of shear and flexure-shear-critical RC elements subjected to increasing axial load is reported herein. The focus is on the effect of vertical load redistribution from axially failing columns on the nonlinear (pre- and post-peak) response of neighboring shear-dominated members. The test results along with an analysis of the recorded deformation, strength, stiffness, and energy dissipation characteristics shed light on the performance of substandard columns under constant and increasing axial load subsequent, or just prior, to failing in shear, thus providing useful insights into the assessment of existing RC structures. [ABSTRACT FROM AUTHOR]

Practical determination of the factor αcc Reinforced and prestressed concrete members must be resistant to all loading scenarios that are possible during their service life. This is independent of the load type and combination as well as the loading time (concrete age at loading) and the load duration. Hence, the time effects of loading are considered in the design value of concrete compressive strength with the factor αcc, which is considered generally as constant values in design code provisions. For the evaluations in ultimate limit state, however, the value of this factor is often a matter of debate. Based on the introduced approach for the differentiated definition of the factor αcc in [1], the potentials of its application are explained and discussed in this paper. [ABSTRACT FROM AUTHOR]

Masonry structures are notoriously vulnerable to horizontal actions caused by earthquakes. Given the high seismicity of the European region, and that the European building stock comprises a lot of masonry buildings, knowledge about their structural response to seismic excitation is particularly important, but at the same time difficult to determine, due to the heterogenous nature of materials and/or constructional techniques in use. An additional issue is represented by the current methods for mechanical properties assessment, that do not provide a reliable framework for accurate structural estimations of existing buildings characterized by different typological properties. Every structure, in other words, should be separately inspected in regard to its mechanical behaviour, based on dedicated approaches able to capture potential critical issues. In this review paper, an insight on the Croatian ARES project is presented (Assessment and Rehabilitation of Existing Structures), including a state-of-the-art of the actual building stock and giving evidence of major difficulties concerning the assessment of existing structures. The most commonly used techniques and tools are compared, with a focus on their basic features and field of application. A brief overview of prevailing structural behaviours and Finite Element numerical modelling issues are also mentioned. As shown, the general tendency is to ensure "sustainable" and energy-efficient building systems. The latter, however, seem in disagreement with basic principles of structural maintenance and renovation. The aim of the ongoing ARES project, in this context, is to improve the current knowledge regarding the assessment and strengthening of structures, with a focus on a more reliable design and maintenance process for existing masonry buildings. [ABSTRACT FROM AUTHOR]

The assessment of existing reinforced concrete structures is one of the major aspects for engineers and practitioners. In particular, existing infrastructures, as bridges and viaducts, are extensively exposed to environmental actions, materials aging, degradation, and variation of magnitude of traffic loads during their service life. Hence, the assessment of existing structural systems assuming the same criteria conceived for the design (i.e., partial factor method—EN 1990) can be too conservative and, sometimes, may lead to unnecessary and expensive structural interventions. In this context, fib Bulletin 80 defines the partial factor methods suitable for the assessment of existing reinforced concrete structures accounting for their residual service life, information from in situ and laboratory tests, measurements of variable actions and reduced target reliability levels according to both economical and human safety criteria. The methodologies proposed in fib Bulletin 80 have been applied to assess the safety of an existing prestressed reinforced concrete bridge built in 90s and located in Italy. The results are compared to the outcomes from the assessment performed according to EN1990 and, finally, limits and advantages of the methodologies proposed by fib Bulletin 80 are discussed. [ABSTRACT FROM AUTHOR]

Recently, Zagreb was struck by a strong earthquake. Damage throughout the city was tremendous due to numerous aged and vulnerable masonry buildings. Many damaged buildings are under a certain level of cultural heritage protection. Hence, reliable assessment and effective rehabilitation are important to preserve cultural significance and mitigate risk for human life. With that in mind, the procedure of a detailed condition assessment of the building under heritage protection is presented. A detailed historical background of the case study building is shown, and observed damage and conducted in situ tests are discussed. The nonlinear static seismic analysis performed in the 3Muri software is extensively elaborated. Four different levels of reconstruction according to new Croatian law are briefly presented. Additionally, several strengthening scenarios are proposed with various strengthening techniques.

Consideration of long term effects in the assessment value of concrete compressive strength – Evaluation of the transferability of approaches defined for the design of new structures Prof. Hegger made a major contribution to development of Eurocode 2 as the German representative in the European Committee for Standardisation CEN/TC250/SC2/WG2 and in his function as chairman of the related German mirror committee. In the next generation of Eurocode 2 rules for the assessment of existing structures will be included, too. For this purpose many different topics on the basics of the design of concrete structures have to be clarified. The aim of the present study is the evaluation of the effect of long term service loading on the factor αcc (coefficient taking account long term effects). For the design of new structures the factor αcc = 0,85 applies. Though, for the assessment of existing structures, based on the investigation of drill cores taken from the structure, the factor αcc is not defined up to now. The main topics which have be evaluated are the effect of subsequent hardening and preload on the compressive strength of drill cores. Generally, it has to be taken into account, that the high level of scattering of the in‐situ concrete compressive strength is opposed to a satisfactory and scientific based verification. However, based on the investigations conducted, the consideration of long term effects on the assessment value of the concrete compressive strength can be recommended. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures realised in earthquake-prone regions are exposed to seismic shakings that may result in significant damage and even lead them to collapse. As well known, high stress concentration occurs at the end of both beams and columns of RC frames, making those members extremely prone to damage. Moreover, beam-to-column joints are particularly sensitive to brittle failure, especially in the cases of unreinforced and unconfined joints. This paper investigates the cyclic response of RC beam-to-column joints. Specifically, it is intended at demonstrating that the decay in shear strength due to cyclic actions can be interpreted in the light of the well-known low-cycle fatigue approach. To do so, cyclic experimental tests on RC joints reported in the scientific literature are collected and analysed. The obtained results show that the parameters governing the shear strength degradation are clearly influenced by both the layout of the RC joints and their actual design criteria. This finding highlights that low-cycle fatigue curves can be considered for describing the decay in shear strength due to cyclic actions; however, further well-documented experimental results are needed to completely identify the relationship between the relevant properties of the RC joint and the resulting low-cycle fatigue curve. [ABSTRACT FROM AUTHOR]

Forming new openings in load-bearing masonry panels is a frequent activity in engineering practice, often accomplished through very simplified design methods despite the complexity of the mechanical behaviour of the masonry and its interaction with the frame. Scientific literature and building codes provide little information. The Italian building code and the local regulation of Tuscany give some dimensional prescriptions and basic guidelines. Different simplified design methods in the literature lead to wide-ranging results. Here, the problem is approached through nonlinear finite-element analyses. The masonry is modelled through a rotating crack constitutive model, and the interaction between steel-frame and masonry, through cohesive-frictional interface elements. Sensitivity analyses are carried out by varying geometrical and mechanical parameters and the responses are compared in terms of capacity curves. The influence of the steel-profile cross-section, the position of the opening within the wall, and the degree of connection between the steel uprights and the masonry are evaluated. The study is extended to three-dimensional structures to determine the impact of the local operation of the opening formation on global behaviour. Based on the results obtained, some indications and guidelines are proposed. [ABSTRACT FROM AUTHOR]

Time-of-flight (ToF) measurements were conducted on twelve 76×226-mm2 in cross-section, 4.52-m long specimens of Norway spruce timber pieces from a dismantled 19th-century building in Barcelona (Catalonia, Spain). Two commercially available acoustic devices were used: the USLab ultrasound device with conical 22 and 45 kHz sensors and the MicroSecond Timer (MST) stress wave device with spike sensors. ToF were obtained for the full-length (4.52 m) specimens in an end-to-end arrangement and for lengths of 0.5, 1, 1.5, 2, 3 and 4 m on the same surface and on opposite surfaces. The differences between the velocities obtained from end-to-end and semi-direct measurements were less than 4.5%. Apparent velocity dependence on length was observed in short-distance measurements. This could be corrected by determining a time lag (tL) from a linear regression between the ToF and the distance. Estimation of the modulus of elasticity (MOE) from the dynamic MOE (MOEdyn) is acceptable (r2=0.45–0.69) depending on the measurement procedure, and the best results for in situ timber are obtained in edge surface velocity. Although modulus of rupture (MOR) estimation from MOEdyn improves slightly when knottiness is included, it has low predictive capacity. [ABSTRACT FROM AUTHOR]

Highlights • Assessment of existing in-service Portuguese roadway composite steel-concrete bridge. • Both numerical and experimental uncertainty sources are taken into consideration. • Experimental data is included through model identification and Bayesian inference. • Applied framework allows an accurate and whole life reliability assessment. • An additional reserve strength was identified through the presented analysis. Abstract This paper presents a framework to assess the safety of existing structures, combining deterministic model identification and reliability assessment techniques, considering both load-test and complementary laboratory test results. Firstly, the proposed framework, as well as the most significant uncertainty sources are presented. Then, the developed model identification procedure is described. Reliability methods are then used to compute structural safety, considering the updated model from model identification. Data acquisition, such as that collected by monitoring, non-destructive or material characterization tests, is a standard procedure during safety assessment analysis. Hence, Bayesian inference is introduced into the developed framework, in order to update and reduce the statistical uncertainty. Lastly, the application of this framework to a case study is presented. The example analyzed is a steel and concrete composite bridge. The load test, the developed numerical model and the obtained results are discussed in detail. The use of model identification allows the development of more reliable structural models, while Bayesian updating leads to a significant reduction in uncertainty. The combination of both methods allows for a more accurate assessment of structural safety. [ABSTRACT FROM AUTHOR]

The assessment of an existing structure to determine its suitability for present and future use entails different sorts of problems than encountered when designing new structures. The differences revolve essentially around the nature of the information available. In existing structures, deteriorated or otherwise, the accuracy of the models used for such assessments can usually be improved by acquiring more data. The most accurate way to find actual load and resistance would be to conduct a probabilistic analysis using site data. This is a time-consuming process, however, calling for a working knowledge of probabilistic methods that may not be suited to everyday use by practising engineers. For this reason, in the past few years various studies have been conducted to develop assessment approaches, compatible with Eurocodes, which include the same verification format as normally applied for designing new structures. In this paper, the application of several of these approaches is illustrated by means of the reliability verification of one of the main beams of the reinforced concrete structure of an industrial building from the 1940s, recently transformed into a cultural centre. The obtained results are discussed and compared to the findings of a full probabilistic analysis.

Time-dependent reliability assessment is a crucial aspect of the decision process for rehabilitation of existing reinforced concrete structures. Since the assessment strongly depends on degradation of materials with time, the paper focuses on the influence of corrosion in reinforcing steel on time-reliability curves of relevant reinforced concrete (r.c.) structures, built in Italy in the 1960s, belonging to different building categories. To realistically represent the probability distribution functions (pdfs) of the relevant properties of reinforcing steel and concrete commonly adopted in the 1960s, stochastic models for steel yielding and concrete compressive strength have been derived, by means of a suitable cluster analysis, from secondary databases of test results gathered at that time in Italy on concrete and steel rebar specimens. This cluster analysis, based on Gaussian mixture models, provides a powerful tool to “objectively” extract material classes and associated probability density functions from databases of experimental test results. In the study, different degradation conditions and several reinforcing steel and concrete classes are considered, also aiming to scrutinize their influence on the time-dependent reliability curves. Finally, to stress the significance of the study, the time-dependent reliability curves so obtained are critically examined and discussed also in comparison with the target reliability levels currently adopted in the Eurocodes.

Masonry structures are notoriously vulnerable to horizontal actions caused by earthquakes. Given the high seismicity of the European region, and that the European building stock comprises a lot of masonry buildings, knowledge about their structural response to seismic excitation is particularly important, but at the same time difficult to determine, due to the heterogenous nature of materials and/or constructional techniques in use. An additional issue is represented by the current methods for mechanical properties assessment, that do not provide a reliable framework for accurate structural estimations of existing buildings characterized by different typological properties. Every structure, in other words, should be separately inspected in regard to its mechanical behaviour, based on dedicated approaches able to capture potential critical issues. In this review paper, an insight on the Croatian ARES project is presented (Assessment and Rehabilitation of Existing Structures), including a state-of-the-art of the actual building stock and giving evidence of major difficulties concerning the assessment of existing structures. The most commonly used techniques and tools are compared, with a focus on their basic features and field of application. A brief overview of prevailing structural behaviours and Finite Element numerical modelling issues are also mentioned. As shown, the general tendency is to ensure “sustainable” and energy-efficient building systems. The latter, however, seem in disagreement with basic principles of structural maintenance and renovation. The aim of the ongoing ARES project, in this context, is to improve the current knowledge regarding the assessment and strengthening of structures, with a focus on a more reliable design and maintenance process for existing masonry buildings.

The management and preservation of structures in our built environment are central and challenging tasks for practicing engineers. Within the CEN member states (European Committee for Standardization), the so-called Eurocodes form the basis of the design and verification of the load-bearing capacity of structures. Current Eurocodes do not contain special recommendations for existing structures, meaning that the principles for new structures are applied. This can lead to an incorrect estimation of the load-bearing capacity within the semi-probabilistic safety concept. A central task within the investigation and evaluation of existing structures is the strength grading of the material in situ using non-/semi-destructive technical devices. Studies show the potential of the ultrasonic time-of-flight measurement in combination with visual evaluation for an improved grading. The information on the material from an improved grading technique can be used to update the material parameters as a target variable using a measured reference variable. In this contribution, test data from a partner project (spruce, pine, and oak) are analyzed, applying the stochastic grading model of Pöhlmann and Rackwitz. It can be shown that different grading techniques influence the updated distribution function of the material strength within the grade. The results depend on the timber species. Perspectives to develop updated models dependent on the knowledge available are shown and discussed.

The aim of this research is to evaluate the effectiveness of a seismic retrofit technique that involves the introduction of energy dissipation devices properly connected to an existing structure through a system of cables and levers, which are employed to amplify total or inter-story drift at device end. One of the main topics related to the introduction of energy dissipation devices, lies in the choice of their optimal setting within the structure to maximize the effectiveness without producing functionality limitations. The achievement of these objectives is, therefore, linked, regardless of the type adopted, to the amount of energy dissipated in each cycle, directly proportional to the displacement magnitude to which the device is subject. Many configurations proposed in the literature and currently adopted in professional practice provide additional dissipation systems variously connected to braces installed inside the structural frame and, therefore, able to exploit the inter-story drift produced by seismic input. The proposed system exploits top displacements of the structure with respect to the foundation level, transferred to the device through a system of cables properly configured and amplified with leverage. This paper represents the first step of the research, in which simple single degree of freedom (SDOF) or two degrees of freedom (2-DOF) models are taken into account to evaluate the effects of the introduction of the proposed system in terms of reducing the seismic demand on the structure, proceeding to a parametric analysis to obtain initial indications for the design of the system in relation to the geometric and inertial characteristics of the original structure.

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Highlights • Rebound number (RN) and ultrasonic pulse velocity (UPV) tests have been carried out on 2 RC walls. • The tests allowed the estimation of the spatial correlation of RN and UPV. • Concrete compressive strength has been estimated by means the SonReb method. • Relevant under- or overestimation of the element concrete strength is caused by correlation. • A simple modification to the standard SonReb procedure is proposed to mitigate the effect of correlation. Abstract In this paper the existence of a spatial correlation on the readings of the rebound hammer tests and ultrasonic pulse velocity tests is firstly investigated by means of experimental evaluations on two RC walls. The effect of this correlation is then transferred in the concrete strength evaluation by means of the well known SonReb method. Monte Carlo simulations, carried out to check the goodness of the evaluation with the SonReb standard procedure, highlighted a relevant probability of under- or over-estimation as well as the possibility of not negligible absolute errors of the expected mean compression strengths for the investigated structural elements. A simple modification to the standard procedure is, finally, proposed in order to take into account the concrete spatial correlation and improve the goodness of the SonReb evaluation. This modification, that basically consists in increasing the relative distance between the location of the individual test readings, allows the reduction of the unconservative maximum percentage overestimation error from roughly 15% to 5%. [ABSTRACT FROM AUTHOR]

This paper presents an effective strengthening strategy to increase the shear capacity of existing reinforced concrete structures. The solution is derived by using the upper-bound theorem of the theory of plasticity, a well-known approach in the design of new structures. It is shown how the solution can be effectively used to not only derive the shear capacity, but also to find out where strengthening reinforcements should be placed. The strategy is exemplified by a strengthening project wherein the cross beams on a three-span concrete bridge have insufficient local and global shear capacity. The cross beams are strengthened with unbonded steel bars, which are installed in drilled holes. First, it is shown how the formulation of kinematically admissible failure mechanisms are easily used in the assessment of the capacity of existing structures. Second, it is shown how the solution is effectively used to find the ideal placement of the steel bars. Finally, the paper presents some considerations on the strengthening method. It is argued that it is necessary to prestress the unbonded post-installed steel bars in order to ensure their concurrent contribution with the existing reinforcement and sliding in the concrete. [ABSTRACT FROM AUTHOR]

This paper offers a new and closer look into the strength anisotropy of concrete by presenting the so far largest experimental programme (290 tests) and by presenting an advanced statistical analysis of the results. The experimental investigation sheds light on the influence of several important design parameters and conditions on the anisotropy. This includes the influence of reinforcement, w / c -ratio, curing time, load history and structural geometry. For this purpose, cores were drilled out at different angles from beam- and slab specimens for compressive testing. The main findings include: a) the reference cylinder strength (i.e. w / c -ratio) does not have a significant influence on the anisotropy when the anisotropy is quantified as an absolute difference between the strength of cores drilled in the two directions; b) the anisotropy in structural members without load history is <5 MPa; c) the anisotropy amounts to 5–10 MPa for members with load history. [ABSTRACT FROM AUTHOR]

In seismic countries of Southern Europe, including Italy, a large stock of existing precast structures for industrial buildings is characterized by beam-to-column dry friction joints. Several failures of this type of structures occurred during recent seismic events, including the Emilia earthquakes in 2012, due to the loss of the friction restraint and shift of the beam out of the support at the top of the column under the combined effects of horizontal and vertical seismic shaking. The seismic behaviour of precast structures with dry-friction joints is investigated based on nonlinear dynamic analysis to support the vulnerability assessment and design of seismic retrofitting interventions of existing industrial buildings. A dry-friction modelling of beam-to-column joints is proposed and case studies are presented to identify the most critical factors affecting the seismic response of precast frame buildings. The results show that flexible systems are more prone to structural failure due to the loss of support of the beam, particularly when the frequency content of the main shock of the seismic excitation includes the natural frequency of the structure in the vertical direction. [ABSTRACT FROM AUTHOR]

Abstract: Partial factor methods for existing concrete structures In literature different methods for the reliability‐based assessment of existing concrete structures have been developed. Nevertheless, a consistent reliability‐based assessment framework and a practically applicable codified approach which is compatible to the Eurocodes and accessible for common structural engineering problems in everyday practice is still missing. Currently the assessment of existing structures is mostly based on simplified procedures based on the partial factor method, commonly applied for the design of new structures. Such an assessment of an existing structure may lead to conservative results and expensive rehabilitation and strengthening measures. Therefore, the fib Task Group 3.1 “Reliability and safety evaluation: full‐probabilistic and semi‐probabilistic methods for existing structures” developed the new fib Bulletin 80 [1] “Partial factor methods for existing concrete structures”. The new Bulletin 80 includes modified partial factors for materials and actions. In the present contribution, based on fib Bulletin 80 [1], two methods for the modification of partial factors for the assessment of existing structures are presented. Furthermore, different methods for the adaption of the target reliability index are described. Finally, the approach is explained, using an example. [ABSTRACT FROM AUTHOR]

Abstract: Systematic recalculation of the bridge inventory of Mecklenburg‐West Pomerania – Interaction between practice and research Since the implementation of the ‘Nachrechnungsrichtlinie' (German recalculation guideline, in short: NRR) in 2011, the assessment of existing road bridges has become increasingly the focus of research. When looking at older structures, a differentiated approach is necessary, because the old bridges have been designed and built according to former standards. To meet these requirements a step by step approach for the recalculation is provided. The continue updating of the guideline, which happened in April 2015 for the first time, will benefit from practice and research. The project ‐scientific and technical supervision for application of the German recalculation guideline on the bridge stock of Mecklenburg‐West Pomerania‐ (WTB) captures this idea and includes a systematic evaluation of the bridge inventory. The following contribution gives an overview about the prioritization of a typical bridge inventory of the former GDR (German Democratic Republic) and the collaboration of authorities, consultant engineers and researchers. [ABSTRACT FROM AUTHOR]

The paper describes a modified cyclic bar model including bond-slip phenomena between steel reinforcing bars and surrounding concrete. The model is focused on plain bar and is useful, for its simplicity, for the seismic analyses of RC structures with plain bars and insufficient constructive details, such as in the case of "60s -"70s Mediterranean buildings. The model is based on an imposed exponential displacements field along the bar including both steel deformation and slip; through the adoption of equilibrium and compatibility equations a stress-slip law can be deducted and simply applied, with opportune operations, to RC numerical models. This study aims to update and complete the original monotonic model published by the authors, solving some numerical inconsistencies and, mostly, introducing the cyclic formulation. The first aim is achieved replacing the imposed linear displacement field along the bar with an exponential too, while the cyclic behaviour is described through a formulation based on the results of parametric analyses concerning a large range of steel and concrete properties and geometric configurations. Validations of the proposed model with experimental results available in the current literature confirm its accuracy and the reduced computational burden, highlighting its suitability in performing nonlinear analyses of RC structures. [ABSTRACT FROM AUTHOR]

The results of material acceptance tests or in-situ tests are a valuable source of information for reliability assessment of existing structures. Huge secondary databases of test results are usually available, coming from different sources, but individual results are often not associated to a given population, so their statistical analysis is a complicated process. In order to solve this problem, the paper presents a methodology that allows to identify homogeneous populations (or material classes), together with their statistical parameters, when mixed in arbitrary and unknown percentages in a secondary database. The methodology is based on the cluster analysis of data applying the Expectation-Maximization algorithm, which allows to figure out individual classes and their characterizing statistical parameters by fitting a Gaussian Mixture Model. The proposed methodology has been applied to a relevant case study, investigating the cubic concrete strength of the Italian production during the 1960s, also using different approaches. The study demonstrates that approximately six concrete classes can be identified, characterized by an almost constant standard deviation of about 4.0–4.5 MPa, in agreement with the results obtained by previous research. As the results obtained with different approaches agree satisfactorily, it can be concluded that, if enough experimental data are available, the proposed procedure is not only suitable for the intended applications, but it is also “robust” enough. [ABSTRACT FROM AUTHOR]

Many post‐tensioned girders of existing bridges contain a low amount of transverse reinforcement. The shear strength of these girders, calculated according to current semi‐probabilistic design codes, like Eurocode 2, is often less than that required in the codes. In this paper, the experimental results of four shear tests on post‐tensioned bridge girders of existing bridges are presented. The specimens were extracted from two different road bridges, both built in 1959. In this paper, the results of this test series are used to analyze the shear behavior and failure modes of existing post‐tensioned bridge structures with a low amount of shear reinforcement. Furthermore, the experimental results are compared with the shear strengths calculated according to various design codes. Finally, the shear behavior is analyzed according to the zone‐based, shear assessment concept with its refined shear models. The calculation results agree well with the data from the experiments. [ABSTRACT FROM AUTHOR]

Abstract: Material characteristics of a historical reinforced concrete bridge – A report about material investigations on existing structures, dedicated to Jürgen Schnell's 65th birthday The determination and characterization of material properties of existing structures is a current focus of research by Prof. Schnell, to whom the article is dedicated. The recent published books of the DAfStb (publication series nr. 616 and 619) provide the expedients for the practicing engineer to determine material strength to evaluate existing structures. Within a historical project on the former civil engineer and professor of the TH Dresden Willy Gehler, the properly oldest reinforced Hennebique concrete bridge of middle Germany was found. The bridge was demolished in 2016 because of a limited flow rate. At least this offers the opportunity to obtain sample material. The investigations on the material behavior were described in the paper as well as a discussion on the difficulty for its determination of values for recalculation. [ABSTRACT FROM AUTHOR]

Collisions with large ungulates cause serious human and animal injuries and significant property damage. Therefore, wildlife crossing structures are increasingly included in new road construction to reduce wildlife–vehicle collisions, while still allowing wildlife to safely cross roads. Recently, state and federal transportation budgets have declined, concomitantly reducing the construction of wildlife crossing structures, which are generally tied to large-scale reconstruction projects that are delayed for decades into the future. Nevertheless, even during times of fiscal constraint or temporal delay, it is still necessary to reduce collisions with wildlife and maintain habitat connectivity. Therefore, it is important to find cost-effective and functional alternatives. Retrofitting roadways with wildlife exclusion fencing that directs animals to existing highway structures (e.g., sufficiently sized bridges and culverts) is a possible cost effective, interim solution that needs further testing. Along Interstate-17 in northern Arizona, we heightened 9.17 km of right-of-way barbed wire fence to 2.4 m to guide elk (Cervus canadensis) to 2 large bridges and 2 modified transportation interchanges. We evaluated occurrence of elk–vehicle collisions, elk use of existing structures, and GPS movements of elk pre- and post-fencing retrofit. Post retrofit, there was a 97% reduction in elk–vehicle collisions for the 9.17 km stretch of road. There were also no increases in collisions at the fence termini (area within 1.61 km from fence ends) nor in the remaining sections, indicating that elk were not simply forced to those areas. We documented a 217% and 54% increase in elk use of the 2 large bridges, but no elk use of the transportation interchanges. GPS relocation data from 31 elk showed a statistically insignificant decrease, from 0.07 to 0.03 crossings per approach pre- and post-fence modification, respectively. Elk road crossings, determined through GPS relocations, were concentrated around the bridge structures rather than being evenly distributed across the treatment sections, and similar to collisions, crossings did not increase on adjacent fence termini. Using the Huijser et al. (2009) estimate of $17,483 for the cost to society of an elk–vehicle collision, the level of collision reduction on this stretch of road will recoup project costs inthat, under certain circumstances, retrofits can in the short-term reduce wildlife–vehicle collisions on roadways that are not scheduled to be reconstructed in the near future. However, for the long-term, areas with significant wildlife– vehicle collisions or habitat fragmentation should have appropriately designed, located, and maintained wildlife crossings with exclusionary funnel fencing.

Frame systems are the preferred structural systems in most seismic regions, where they are sometimes also combined with braces or walls. On the other hand Chile, one of the most seismically active countries in the world, is an exception to this practice. Any Chilean residential building higher than 5 stories is almost completely made up of reinforced concrete shear walls. Surprisingly, only 2% of the residential building inventory subjected to the 2010 Chile earthquake (M w 8.8) suffered severe damage, even though many structures were affected by ground accelerations larger than those prescribed in the Chilean seismic design code. This observation suggests that there is a large (and unintended) overstrength in this type of buildings. In a previous study, the authors showed that some of the traditional sources of overstrength mentioned in the literature could explain the lack of damage in low rise buildings but not in taller structures. Motivated by this observation, representative tall buildings were reanalyzed using more realistic models (e.g., flexural capacity of the walls assessed by fiber models) in order to get more insight into their actual seismic capacity. Two actual buildings of 17 and 26 stories that survived with no damage the 2010 Chile earthquake were analyzed by response history analysis. Results show that consideration of wall flanges (usually omitted in practice) cannot explain the lack of damage. On the other hand, it is observed that good performance might be a consequence of possible foundation uplift. Finally, the analyses also suggest that, even when there is no damage, elastic analysis has limitations to reproduce the actual observed behavior. [ABSTRACT FROM AUTHOR]

Many countries are experiencing an increasing need of checking the safety of existing structures. The assessment of structural capacity of RC structures strictly depends on the in situ compressive strength of concrete. The evaluation of this property is typically carried out by means of destructive tests on concrete cores taken from the structure. The experimental data is then interpreted using a relevant code to obtain a design strength value according to the required percentile and confidence. In this paper the principal international standards that deal with the statistical interpretation of data from concrete core tests are presented. Since it is reasonable to assume that concrete strength is a realization of a random field, the assumption of statistical independence of core test data is questioned. An extension of the classical theory of tolerance limits in the case of normally distributed correlated samples is thus proposed. Finally, application examples of this methodology are provided to illustrate some important implications of the spatial correlation of core test values on concrete strength estimations. [ABSTRACT FROM AUTHOR]