Shear design of HSC beams with combination of links and horizontal web steel

The existing recommendations in Eurocode 2 and the British Code of Practice for the shear design of beams are derived from research conducted essentially on normal-strength concrete (NSC) with cube strengths up to 50 MPa, and it was found that the shear strengths of high-strength concrete (HSC) members made with limestone aggregate are below the characteristic resistances of identical NSC members. Previous experimental tests have also shown that significant differences exist in the angle of crack of shear failure of NSC and HSC. This paper presents data from five beam tests, which demonstrate that HSC with limestone aggregate has a reduced shear strength compared with NSC made with gravel and thus shows a gap in knowledge in the design approach to shear resistance of HSC beams. Previous investigations have suggested that horizontal web steels can contribute to the overall shear resistance of a reinforced concrete member in conjunction with the other constituents, concrete, tension and shear steel. The paper also presents data from tests on 11 beam tests and shows that the shear resistance of HSC beams is highly dependent on dowel action resulting from horizontal web bars positioned at the centre of the depth of the beam. Past attempts to quantify this dowel action are investigated and an improved design rule is proposed

Effect of temperature and acidity of sulphuric acid on concrete properties

Concrete corrosion caused by sulphuric acid attack is a known phenomenon in sewer systems, resulting in significant economic losses and environmental problems. However, there is a scarcity of reported laboratory simulations and experimental work investigating the contributing factors controlling the corrosion. In this EPSRC (Engineering and Physical Sciences Research Council, UK) funded investigation the effect of temperature and the acidity of sulphuric acid solution on concrete specimens extracted from brand new concrete sewers has been investigated. In this investigation the concrete samples are submerged in three sulphuric acid solutions (pH = 0.5, 1 and 2) for 91 days under different temperatures (10ºC, 20ºC and 30ºC). Mass loss and compressive strength of the concrete specimens were tested and recorded at 7, 14, 28, 42, 56 and 91 days providing interesting data for visualising the changes taking place in the concrete samples (change in properties) during the time of immersion. The results revealed that samples overall mass increased at the early stages of the corrosion process. It also was observed that the overall mass of the samples decreased significantly at the later stages of the testing process with respect to the acidity of the solutions used. Although the change in temperature did not have a significant effect on the compressive strength of the tested samples, rise in temperature however, had considerable effect on the mass loss of the concrete samples which were immersed in the most aggressive solution (i.e., pH=0.5 and temperature = 30oC) at 91 days. This research clearly demonstrated a high correlation between the acidity of the solution and the rate of corrosion with respect to time

Monitoring CO2 and H2S emission in live Austrian and UK concrete sewer pipes

Corrosion of concrete sewer pipes induced by sulfuric acid is an acknowledged problem and a ticking time-bomb to sewer operators. Whilst the chemical reaction of the corrosion process is well-understood, the indirect roles of other parameters in the corrosion process which are found in sewer environment are not highly reflected on. This paper reports on a field studies undertaken in Austria and United Kingdom, where the parameters of temperature, pH, H2S and CO2 were monitored over a period of time. The study establishes that (i) effluent temperature and pH have similar daily pattern and peak times, When examined in minutes scale, (ii) H2S and CO2 have an identical hourly pattern, (iii) H2S instant or shifted relation to effluent temperature is governed by the root mean square value of CO2

An entropy-based analysis of GPR data for the assessment of railway ballast conditions

The effective monitoring of ballasted railway track beds is fundamental for maintaining safe operational conditions of railways and lowering maintenance costs. Railway ballast can be damaged over time by the breakdown of aggregates or by the upward migration of fine clay particles from the foundation, along with capillary water. This may cause critical track settlements. To that effect, early stage detection of fouling is of paramount importance. Within this context, ground penetrating radar (GPR) is a rapid nondestructive testing technique, which is being increasingly used for the assessment and health monitoring of railway track substructures. In this paper, we propose a novel and efficient signal processing approach based on entropy analysis, which was applied to GPR data for the assessment of the railway ballast conditions and the detection of fouling. In order to recreate a real-life scenario within the context of railway structures, four different ballast/pollutant mixes were introduced, ranging from clean to highly fouled ballast. GPR systems equipped with two different antennas, ground-coupled (600 and 1600 MHz) and air-coupled (1000 and 2000 MHz), were used for testing purposes. The proposed methodology aims at rapidly identifying distinctive areas of interest related to fouling, thereby lowering significantly the amount of data to be processed and the time required for specialist data processing. Prominent information on the use of suitable frequencies of investigation from the investigated set, as well as the relevant probability values of detection and false alarm, is provided

A spectral pedestrian-based approach for modal identification

The dynamic behaviour of footbridges is characterised by modal properties such as natural frequencies, mode shapes, damping ratios and modal masses. Their estimation via modal tests often requires expensive or difficult-to-operate equipment (e.g. shaker and instrumented impact hammer) or, sometimes unavailable high signal-to-noise ratios in tests relying on natural (e.g. wind, airborne noise and ground-borne vibration) excitation. In addition, the modal properties determined in modal tests do not necessarily apply to the structure under pedestrian traffic in case of amplitude-dependent frequencies and damping ratios. The current work proposes a novel approach that stands in contrast to the widely used tests, based on modal identification using an excitation induced by a single pedestrian. In order to account for estimation and observation uncertainties, the relationship between the power spectrum of the response and its modal properties is described with a likelihood function. It is shown that it is possible to reliably estimate modal properties using pedestrian walk forces measured in the laboratory, and dynamic responses measured when the same pedestrian is crossing a footbridge at timed pacing rates. The approach is validated using numerical and field data for a 16.9 m long fibre reinforced polymer footbridge. This work paves a new way for simple and low cost modal testing in structural dynamics

A GPR signal processing procedure for detecting rail ballast conditions by an entropy-based approach

Ballasted railroads are among the most common construction types in railway engineering due to the effective drainage capability and load-bearing capacity achieved at relatively low construction costs. Rail ballast is usually made of uniformly-graded coarse aggregates derived from crushed rocks of differing geological nature, mostly granite, basalt and limestone. According to Selig and Waters [1], several categories can be identified as principal source mechanisms of fouling, namely, the breakdown of ballast, the infiltration from ballast surface (downward migration of coal dust from commercial trains) and the upward migration of clay fines from the subgrade, are the major causes of fouling. Notwithstanding the increased costs of maintenance, fouling occurrence may dramatically impact on the safety and operation of railways [2]. In view of this, effective health monitoring and early-stage detection of fouling is mandatory to allow significant reduction of both unsafe events and maintenance costs. Within this context, non-destructive testing (NDT) techniques are becoming more important in the health monitoring of railways

A pedestrian-based forced vibration approach for modal identification

A wide number of applications in vibration analysis rely on estimation of modal properties, such as natural frequencies, mode shapes, damping ratios and modal masses [1]. Identified modal parameters form an information baseline for model updating [2], sensor placement, damage detection [3] and structural performance evaluation [4]. Thus, the relevance of modal testing keeps increasing, particularly for slender and wobbly structures such as long bridges. At the same time, modal identification often relies on expensive and difficult-to-operate technical equipment, such as shakers or impact hammers. Other drawbacks of these methods include high sensitivity to non-linearities, timeconsumption and susceptibility to human-structure interaction effects. As a consequence, this work investigates the applicability of a new spectral approach for modal identification in slender structures. The approach is fast, cost-effective and easy-to-perform. It questions if is it possible to identify modal properties, with a reliability comparable to standard modal tests, using only a human induced excitation. The identification process requires two main inputs: recordings of structural responses under passage of a given pedestrian at a timed pacing rate; and the pedestrian’s walk forces at the same pacing rate (which can be recorded with an instrumented treadmill). Validation of the methodology is illustrated with a 16.9 m long fiber reinforced polymer footbridge, instrumented with accelerometers, on which standard modal tests have been performed. One of the most significant aspects of the proposed approach is its probabilistic treatment of the identification process, which allows to learn the modal properties from data, while accounting for their estimation variability and measurement noise. Moreover, the human excitation is described with a power spectral density model, based on recorded pedestrian walk forces. In essence, a complex Gaussian log-likelihood function of the dynamic response power spectrum is established and then sampled with the Metropolis–Hastings [5] algorithm. Future developments aim to also account for identification bias. Results indicate that the pedestrian-based approach can identify natural frequencies and damping ratios with a reliability comparable to reference values, obtained with an impact hammer modal test. On the other hand, modal masses are biased relatively to reference values. However, it is noted that even on standard tests, modal masses pose a challenging identification problem. Consequently, the pedestrian-based approach developed in this work is believed to pave a new way for modal identification in structural dynamics. [1] J. Brownjohn, P. Reynolds, S.-K. Au, D. Hester, and M. Bocian, “Experimental modal analysis of civil structures: state of the art,” presented at the SHMII – 7th International Conference on Structural Health Monitoring of Intelligent Infrastructure, 2015. [2] A. Jesus, P. Brommer, R.Westgate, K. Koo, J. Brownjohn, and I. Laory, “Bayesian structural identification of a long suspension bridge considering temperature and traffic load effects,” Structural Health Monitoring, pp. 1–14, Sep. 2018. [3] A. Jesus, P. Brommer, R.Westgate, K. Y. Koo, J. Brownjohn, and I. Laory, “Modular Bayesian damage detection for complex civil infrastructure,” JCSHM, no. Current Advances in Structural Health Monitoring, Dec. 2018. [4] A. Jesus, P. Brommer, Y. Zhu, and I. Laory, “Comprehensive Bayesian structural identification using temperature variation,” Engineering Structures, vol. 141, pp. 75–82, Jun. 2017

Concrete sewer pipe corrosion induced by sulphuric acid environment

Corrosion of concrete sewer pipes induced by sulphuric acid attack is a recognised problem worldwide, which is not only an attribute of countries with hot climate conditions as thought before. The significance of this problem is by far only realised when the pipe collapses causing surface flooding and other severe consequences. To change the existing post-reactive attitude of managing companies, easy to use and robust models are required to be developed which currently lack reliable data to be correctly calibrated. This paper focuses on laboratory experiments of establishing concrete pipe corrosion rate by submerging samples in to 0.5 pH sulphuric acid solution for 56 days under 10ºC, 20ºC and 30ºC temperature regimes. The result showed that at very early stage of the corrosion process the samples gained overall mass, at 30ºC the corrosion progressed quicker than for other temperature regimes, however with time the corrosion level for 10ºC and 20ºC regimes tended towards those at 30ºC. Overall, at these conditions the corrosion rates of 10 mm/year, 13,5 mm/year and 17 mm/year were observed

The application of Ground-Penetrating Radar to transportation engineering: recent advances and new perspectives (GI Division Outstanding ECS Award Lecture)

Ground-penetrating radar (GPR) is one of the most acknowledged and established non-destructive testing (NDT) techniques within the context of the health monitoring and assessment of transportation infrastructures. GPR is being increasingly used for the effective management of infrastructural assets as it weakens the case for using other destructive monitoring methods, such as digging holes, and allows for rapid and reliable detection of many causes of the subsurface damage. Thereby, its usage favours the optimisation of the economical expenditure for the effective maintenance of great infrastructures as well as it improves the public safety by preventing or not raising the risk of accidents. GPR has been used in highway, railway and airfield engineering as well as for the monitoring of critical infrastructures, such as bridges and tunnels. It has found established use in the assessment of the geometric properties of the subsurface, such as in the case of the evaluation of the pavement layer thicknesses, or the size of the rebars in concrete-made structural components. Major physical-based investigations have been focused on the evaluation of the moisture ingress in flexible road pavements and in concrete structures, as well as on the detection of the rebars corrosion caused by the ingress of chloride. The majority of these parameters are evaluated using methods of signal analysis and data processing based on the signal in the time domain. The sophistication of the hardware and software of the GPR systems over the last few years as well as the recent advances achieved in the research have contributed to raise the high potential of this non-destructive technique and paved the way towards new application areas in transportation engineering. In particular, GPR is nowadays finding major application when used with complementary non-destructive testing techniques, although it has still proved to provide reliable results in various self-standing applications. This work aims at presenting the recent advances and the new perspectives in the application of GPR to transportation engineering. This study reports on new experimental-based and theoretical models for the assessment of the physical (i.e. clay and water content in subgrade soils, railway ballast fouling) and the mechanical (i.e. the Young’s modulus of elasticity) properties that are critical in maintaining the structural stability and the bearing capacity of the major transport infrastructures, such as highways, railways and airfields. With regard to the physical parameters, the electromagnetic behaviour related to the clay content in the loadbearing layers of flexible pavements as well as in subgrade soils has been analysed and modelled in both dry and wet conditions. Furthermore, it is discussed a new simulation-based methodology for the detection of the fouling content in railway ballast. Concerning the mechanical parameters, experimental based methods are presented for the assessment of the strength and deformation properties of the soils and the top-bounded layers of flexible pavements. Furthermore, unique case studies in terms of the methodology proposed, the survey planning and the site procedures in rather complex operations, are discussed in the case of bridges and tunnels inspections

Transport infrastructure monitoring by data fusion of GPR and SAR imagery information

In order to maintain the highest operational safety standards, it is crucial that surface and structural deformation caused by geophysical natural hazards and human-related activities in linear transport networks (such as highways and railways) are monitored and evaluated. Today, Ground Penetrating Radar (GPR) is a well-established technology among the available non-destructive testing (NDT) methods for the collection of ground-based information. Concurrently, the space-borne Interferometric Synthetic Aperture Radar (InSAR) is another well-known viable methodology for large-scale investigations of road network surface deformations. However, it is fair to comment that the potential of this method in the area of transport infrastructure monitoring has not yet been sufficiently explored. Within this context, this research demonstrates the viability of integrating InSAR and GPR for monitoring transport assets at network level. The main theoretical and working principles of the two above-mentioned methodologies have been presented and discussed, and the advantage and drawbacks of each technique have then been analysed. The final section of the paper examines a recent experimental activity carried out on a real-life railway located in Puglia, Southern Italy. Test outcomes prove the viability of the proposed data fusion methodology for monitoring the health of transport assets at network level