Structural Engineering Institute Research Articles

Vertical Track–Bridge Interaction in Railway Bridges with Ballast Superstructure: Experimental Analysis of Dynamic Stiffness and Damping Behavior

Realistic vibration predictions of railway bridges during high-speed train crossings require reliable dynamic input parameters for the applied calculation model. In particular, the dynamic stiffness and damping properties of the ballast superstructure for the mathematical consideration of the vertical track–bridge interaction (TBI) significantly influence the generated calculation results. However, due to a striking scattering of model-related characteristic values available in the literature, adequate and realistic consideration of the dynamic properties of the vertical TBI in vibration predictions is associated with considerable uncertainties. This uncertainness illustrates the need to determine experimental-based and reliable characteristic values. For targeted and isolated research of dynamic characteristics of vertical TBI, a unique large-scale test facility was developed at the Institute of Structural Engineering at TU Wien, which replicates a section of ballast superstructure on a railway bridge on a scale of 1:1 and excited to vertical movements. This paper presents the essential results and findings from the experiments, focusing on determining the ballast superstructure’s dynamic stiffness and damping characteristics, which can subsequently be implemented in practical applications for vibration predictions. As a result of the experiments, model-related dynamic stiffness and damping parameters are provided to describe the vertical TBI. In addition, the experiments are used to identify destabilization processes occurring in the ballast superstructure as a result of vertical vibrations. The investigations include the vertical TBI’s displacement and acceleration behavior and the track’s settlement behavior due to the entire structure’s vertical movements. These investigations allow for assessing the currently valid, internationally, and nationally normatively prescribed permissible accelerations for railway bridges due to train crossings. The conclusion is that short-term excessive vertical accelerations of the ballast superstructure caused by train passage do not destabilize the ballast bed or considerably change the track position.

Investigation into the Mechanical Properties of Commercial Sandcrete Blocks Produced in Nigeria: A Case Study of Warri Metropolis

This study investigated the extent to which the mechanical strength of commercially produced sandcrete blocks in Delta State, Nigeria, conforms to recognized international standards. Fifty sandcrete blocks (28 curing days) were sampled from ten known sandcrete block manufacturers in Warri municipal area, five blocks from each manufacturer. The compressive strength of the blocks was determined in accordance with the American Society for Testing and Materials (ASTM) International guidelines. The results showed that the compressive strength of all the blocks failed to meet the Nigeria Industrial Standard (NIS) benchmark for load loading sandcrete block, while only 20% of the blocks attained NIS requirement for non-load bearing walls. Field observation revealed that poor mixing ratio of the sandcrete; inconsistencies in the batching method and sand used in the production of the sandcrete blocks were responsible for the poor quality (low compressive strength) of the sandcrete blocks manufactured in the region. The findings of this study underscore the importance for the Nigerian Institution of Structural Engineers, to rigorously monitor the strength of sandcrete blocks made in Nigeria to ensure that their quality meets internationally recognized standards. This will reduce the occurrence of structural damage in Nigeria, due to the use of low quality blocks for wall constriction.

How to approach the assessment of an existing building

Assessing the safety of an existing building needs a very different mindset from designing a new building. This article discusses how to approach the assessment and some of the key questions which need to be answered, such as the extent to which we can rely on past performance and what margin of safety is acceptable. The article does not claim to have all the answers, but it is hoped these can be covered in forthcoming guidance from the Institution of Structural Engineers.

Deck Slab Elements for the Accelerated Construction of Steel–Concrete Composite Bridges

Various methods have been developed to produce deck slabs for steel–concrete composite bridges. Usually, the deck slabs are cast with in situ concrete using a formwork carriage, resulting in construction progress of 15 to 25 m of deck slab per week. A new construction method was developed at the Institute of Structural Engineering (TU Wien), which enables the swift erection of the concrete deck slab. This method employs precast deck slab elements with reinforced concrete cross-beams which span in the transverse direction. With this new construction method, producing up to two deck slab sections of 15–25 m per day becomes possible. Further, the performance of novel reinforcement detailing required for the precast deck slab elements is investigated by structural testing. The experiments consist of eight load-bearing tests on four specimens which represent sections of the element during casting and after completion. The investigated parameters in series 1 are the length and spacing of loops, used for protruding longitudinal bars enclosure. In series 2, the enclosure of the shear reinforcement and the height of the cross beams are varied. The results show that the targeted bending capacity could be reached in all tests with no signs of premature failure due to detailing reasons. Based on the experimental results, the feasibility of the new approach is shown and recommendations for detailing are given.

Viewpoint: Fifteen years on – where are we today?

In 2008, Sarah Buck became the first female President of the Institution of Structural Engineers. Fifteen years later, she reflects on what has changed in this time and what's next for the industry.

President's Inaugural Address: Working together for a creative and collaborative future

President of The Institution of Structural Engineers for 2018, Faith Wainwright MBE, discusses climate change, urbanisation and demographic change in the context of the profession.

Competence, the UK Building Safety Act, and the Institution of Structural Engineers: a timely update

IStructE CEO Martin Powell provides an update on how the new Building Safety Act will affect the profession and sets out a proposal for a specialist Building Structures Register.

Modern cladding systems for big sheds: The emerging state of the art

Stressed skin theory was first introduced in the 1960’s and intensive development continued until the mid-1980’s. This development was characterised by extensive research into the behaviour of low-rise portal frame structures clad with a single skin of profiled metal sheeting. The resulting state of the art was formalised in ECCS (1995). Since then, frames have become much taller and more slender while alternative cladding systems have proliferated. About 10 years ago, the construction industry in the UK was shaken by a small number of failures in the roofs of ‘Big Sheds’ clad with sandwich panels. Investigation by numbers of experts was inconclusive and non-disclosure orders (NDO’s) were issued by the companies concerned. In the UK, the Standing Committee on Structural Safety (SCOSS) was informed of this and, after discussion with the Institution of Structural Engineers issued an Alert entitled ‘Effects of scale’ (SCOSS, 2018). This drew attention to the fact that validation of our current design rules has been largely based on years of satisfactory building performance. However, such evidence may not be indicative of satisfactory performance as structures increase in scale. In deference to the NDO’s, a research program has been commenced based entirely on structural mechanics without making any direct reference to either forensic evidence from the sites of the failures or test results etc. that are not in the public domain. This is one of the papers arising from this research. It recognises significant deficiencies in the design procedures in the European Recommendations (ECCS, 1995) and the need for a full, non-linear, 3D numerical analysis of the complete clad structure. This, in turn, has resulted in the development of the ‘component method’ of analysis for structure cladding interaction problems that concentrates on the development of numerical models together with the performance of their ‘components’. The main alternative cladding systems are considered in turn and their characteristics and potential failure modes identified.

New SEI/ASCE Disproportionate Collapse Mitigation Standard

For the past several years, a committee of the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE) has been drafting a new standard addressing analyses and design for the mitigation of disproportionate collapse of buildings and other structures. It strives to be a performance standard, providing guidance for analyses, acceptance criteria, quantification of anticipated collapse, detailing, and performance verification. The draft of the standard has been subjected to a series of committee ballots, and presently is being formatted for Public Ballot. Therefore, it still is a draft that could undergo revisions. This paper describes the history of the standard and summarizes its contents as they stand as of this writing.

An Evaluation of the Impact of Databases on End-of-Life Embodied Carbon Estimation

The growing awareness of the need to minimise greenhouse gas (GHG) and mitigate climate change has resulted in a greater focus on the embodied carbon (EC) of construction material. One way to ensure the environmental impact of building activities is minimised to a reasonable level is the calculation of their EC. Whilst there are a few studies investigating the role of embodied carbon factor (ECF) databases on the accuracy of EC calculation from cradle to gate, very little is known about the impact of different databases on the end-of-life (EoL) EC calculation. Using ECFs derived from the UK Department for Business, Energy and Industrial Strategy (BEIS), the Royal Institute of Chartered Surveyors (RICS) default values and the Institution of Structural Engineers (IStructE) suggested percentages for different elements of a building’s lifecycle stages, this study presents the impact of different data sources on the calculation of EoL EC. The study revealed that a lack of EoL ECFs databases could result in a significant difference of about 61% and 141% in the calculation of EC.

Power stations, bridges and skyscrapers: forgotten figures in structural engineering history. Part 2: Florence Taylor and Mary Irvine - first women members of the Institution of Structural Engineers

The 2020 James Sutherland History Lecture given by Steven Brindle covered the emergence of structural engineering as a profession over the last 200 years. This paper covers the same period but from a slightly different perspective, looking at some early women in structural engineering. The paper is in two parts. The first, by Nina Baker, provided some general context and an overview of some of the better known women engineers of this period. The second part, by Fiona Cobb, covers new research into two figures of particular interest to the Institution of Structural Engineers. For this, there are two candidates as ‘first woman’ of the Institution: Florence Taylor (1926) and Mary Irvine (1947) and they are of particular interest as we approach their Institution anniversaries. The centenary of Taylor’s membership will be in 2026 and the 75th anniversary of Irvine’s will be in 2022.

On the Load‐Bearing Behaviour of the Steel‐Concrete‐Steel Composite (SCSC) Plate

AbstractThe presented innovative steel‐concrete‐steel composite (SCSC) plate is being researched at TU Wien, Institute of Structural Engineering, Research Unit Steel Structures. The research aim is to use the SCSC plate for single‐track short‐span railway bridges in Austria. The SCSC plate is projected to be a load‐bearing structure in transverse direction, transferring the loads to the main steel girders of the cross section. Based on finite element analyses using ABAQUS, the complex load‐bearing behaviour of the SCSC plate will be described in this paper. In addition, an engineering model will be presented to reproduce the ABAQUS calculation results. With a spring framework model it is possible to consider cyclic loading and inelastic slip. This yields an increase of the global vertical displacements, which are discussed in the paper.

Power stations, bridges and skyscrapers: forgotten figures in structural engineering history. Part 1: Becoming a professional - the contexts of some pioneering women working in structural engineering

The 2020 James Sutherland History Lecture given by Steven Brindle covered the emergence of structural engineering as a profession over the last 200 years. This paper covers the same period but from a slightly different perspective, looking at some early women in structural engineering. The paper is in two parts. The first is by Nina Baker and provides some general context and an overview of some of the better-known women engineers of this period. The second is by Fiona Cobb and will cover new research into two figures of particular interest to the Institution of Structural Engineers. For this, there are two candidates as ‘first woman’ of the Institution: Florence Taylor (1926) and Mary Irvine (1947). They are of particular interest as we approach their Institution anniversaries. The centenary of Taylor’s membership will be in 2026 and the 75th anniversary of Irvine’s will be in 2022.

Optimized reinforcement in longitudinal joints of segmental tunnel linings

AbstractWhen building tunnels using segmental lining, the segmental lining takes over the supporting role of the excavated soil. With the workspace in tunnel construction being very constricted the circular, segmental linings are divided into small segments called tubbings which are assembled by a tunnel boring machine. This kind of construction results in numerous longitudinal and circumferential joints. The loading situation for the longitudinal joints is typically dominated by the compressive normal forces combined with relatively small bending moments. The thickness of the tubbings usually depends on the longitudinal joints of the individual segments. The cross‐sectional area of the tubbings has to be reduced at the joints in order to avoid spalling of the concrete leading to higher compression in the joints themselves. The Institute of Structural Engineering of TU Wien developed a new reinforcement design for tubbings with strengthened longitudinal joints. With a patent application pending, the newly designed joints were manufactured and tested demonstrating that the TU Wien proposal significantly increases the load‐bearing capacity of the tubbings in comparison to conventional tubbing solutions. The very satisfying results, obtained from the large‐scale tests of the newly developed joint design, show great potential for the construction of tunnels with thinner tubbings in the near future.

The rise of the civil engineering profession in Britain

In this paper, based on his James Sutherland History Lecture delivered to the Institution of Structural Engineers in 2020, Steven Brindle provides a brief history of civil engineering in Britain, charting its development from hydraulic projects and early attempts to apply intellect to structural design in the 17th century, through a great commercially driven boom in the Georgian era, to the foundations of the modern profession in the late 18th and early 19th centuries.

An introduction to The Structural Carbon Tool

Penny Gowler and Will Arnold preview a new embodied carbon tool that has been developed by Elliott Wood and the Institution of Structural Engineers.

Bayesian optimization algorithm based support vector regression analysis for estimation of shear capacity of FRP reinforced concrete members

The use of fiber-reinforced polymer (FRP) rebars in lieu of steel rebars has led to some deviations in the shear behavior of concrete members. Several methods have been proposed to forecast the shear capacity of such members. Nonetheless, there are differences in the methods of considering the various parameters affecting shear capacity, and some of them provide widely scattered and conservative results. This paper presents a hybrid of the Bayesian optimization algorithm (BOA) and support vector regression (SVR) as a novel modeling tool for the prediction of the shear capacity of FRP-reinforced members with no stirrups. For this purpose, a large dataset of simply supported beams and unidirectional slabs reinforced with FRP were utilized. The model performance was assessed using several statistical performance indicators and compared with the Japan Society of Civil Engineers (JSCE), British Institution of Structural Engineers (BISE), Canadian Standard Association (CSA), and American Concrete Institute (ACI) design codes and guidelines, as well as some other artificial intelligence (AI) models. For development of the model, all the hyperparameters, i.e., kernel function type, epsilon, box constraint, and kernel scale, were optimized using the BOA technique. The k-fold cross validation approach was utilized to avoid overfitting of the model. It was found that the mean, median, standard deviation, minimum, maximum, and interquartile range of the developed hybrid model predictions are very close to the experimental results. The predicted results overlap the experimental data with a coefficient of determination of 95.5%. The plot of relative deviations and residual plots are scattered around the zero reference line with low deviation, which indicates that the model is reliable and valid. The error terms (e.g., mean absolute error, root mean square error) obtained for all specimens were 4.85 and 11.03, which are very low values. The correlation coefficient (R) and fractional bias (FB) were found to be 0.977 and 0.0033, which are very close to 1 and 0, respectively, thus implying a reliable prediction. The comparative investigations with other codes and guidelines show that the hybrid BOA–SVR model predictions are more accurate and robust than those of the other models.

Longitudinal joints of tubbings with newly designed high‐strength reinforcement

AbstractContinuous tunneling using a tunnel‐boring machine is a very popular method when it comes to the construction of large tunnel projects. The use of precast reinforced concrete elements, called tubbings, is a highly economical way to secure the tunnel post excavation. Unfortunately, a loss of the load‐bearing capacity has been observed in the past in the joints between the tubbings. Reasons for that are among others the required reduction of the cross section in the longitudinal joint area and, above all, the high normal compressive forces that arise due to soil pressure. This paper describes experimental testing of longitudinal joints of tubbings conducted at TU Wien. The increase of the load‐bearing capacity of a newly designed and optimized tubbing with high‐strength joint‐compressive reinforcement, which was developed and patented by the Institute of Structural Engineering at TU Wien, is presented. The high‐strength steel is characterized by its high yield strength of 670 MPa, as well as the very large available bar diameters of up to 75 mm. This new optimized tubbing enables the production of thinner tubbings compared to conventional designs, and can thus achieve a reduction in material, transport and excavation costs.

Simulation of a SCSC plate with a spring framework model including the effects of inelastic slip

AbstractThe research into an innovative steel‐concrete‐steel composite (SCSC) plate presented here is being carried out in the Steel Structures Research Unit of the Institute of Structural Engineering at TU Wien. The aim of the research is to use the SCSC plate for single‐track, short‐span railway bridges in Austria. The SCSC plate is designed to be a loadbearing structure in the transverse direction, transferring the loads to the main steel girders of the bridge cross‐section. An engineering model will be presented in this paper to reproduce the results of the ABAQUS finite element analysis software [1]. Using this simple framework model, which includes springs, it is possible to consider cyclic loading and inelastic slip, too. This results in an increase in the global vertical displacements and a change to the internal forces, which are discussed in the paper.

Experimental investigation and analytical modelling of shear strength of thin walled textile-reinforced UHPC beams

The combination of two high performance materials, ultra-high performance concrete and carbon reinforcement, allows for the construction of efficient, durable thin-walled structural elements. In order to investigate the shear behaviour of such elements a test series on thin-webbed textile reinforced T-beams was planned and carried out at the Institute of Structural Engineering at TU Wien. In the experiments the efficiency of carbon textile reinforcement grids with different impregnation materials used as shear reinforcement was analysed. Furthermore, the shear span to effective depth ratio as well as the effect of prestressing on the shear carrying capacity was investigated. This article describes the experimental programme and shows the test results. The evaluation of the results indicates a higher shear performance of beams with lower-tex sand coated, acrylonitrile-styrene-acrylate copolymers impregnated textile fabrics than with Heavy-Tow grids with an epoxy resin impregnation. For the case of prestressing the carbon fibre reinforced polymer an additional increase of the shear carrying capacity of the thin-walled carbon textile reinforced structures was verified.