Current Design Codes Research Articles

Estimation of the shear strength of UHPC beams via interpretable deep learning models: Comparison of different optimization techniques

In this article, optimized deep learning (DL) models with different algorithms are adopted to estimate the shear strength of rectangular ultra-high performance concrete beams (UHPC-Bs) in order to overcome the challenges in traditional mechanics-based approaches. Long short-term memory (LSTM) and gated recurrent unit (GRU) are chosen as the DL models, whereas the recent popular optimization algorithms are phasor particle swarm optimization (PPSO), dwarf mongoose optimization (DMO), mountain gazelle optimizer (MGO), and atom search optimization (ASO). A thorough and reliable dataset of 244 UHPC-Bs test results with ten input features has been used to construct the hybrid DL models. The performance of the optimized hybrid LSTM and GRU models with different algorithms is extensively assessed and compared based on various statistical metrics, error, and score analyses. Then, the model with the best estimation performance is determined and compared with the mechanics-based formulas in the current international design codes. Additionally, Shapley additive explanations (SHAP) analysis is used to assist in the interpretability of DL models and to reveal the effects of input features that contribute to the model's estimation. According to the results of the present work, all DL models successfully estimate the shear strength of UHPC-Bs. Among these models, the MGO-LSTM model stands out compared to the other models in terms of several performance measures for both the training and testing phases, like a higher R2 value, lower RMSE, MAPE, and MAE values, as well as a smaller error ratio and a higher final score. The performance of the algorithms applied to optimize the hyper-parameters of the LSTM and GRU models can be ranked as follows: MGO > DMO > PPSO > ASO. Moreover, a graphical user interface (GUI) was constructed based on the best estimation model that was built so that the shear strength of UHPC-Bs could be estimated in real-world situations without the need for any extra software or tools. This enables more users to quickly and easily estimate the shear strength of UHPC-Bs, optimize design processes, and decrease experimental testing costs.

Shear strength model of FRP-reinforced concrete beams without shear reinforcement

The current design codes for evaluating the shear strength of concrete beams reinforced with fiber-reinforced polymer (FRP) bars predominantly rely on a semi-empirical approach through test data calibration without a robust theoretical background. This approach may lead to either overestimation or underestimation, resulting in significant scattering in strength predictions. This study proposed a modified approach to enhance the existing unified shear-strength model developed for steel-reinforced concrete (RC) beams based on the compression zone failure mechanism, for predicting the shear strength of FRP-RC beams without shear reinforcement. The proposed model integrates strain and stress approaches, accounting for the distinctive characteristics associated with FRP reinforcement. Additionally, the overall shear resistance capacity of the FRP-RC beam is considered as the sum of contributions from the intact concrete of the compression zone and the aggregate interlock mechanism. The reliability of the proposed model is verified by comparing its predictions with a comprehensive database comprising 264 FRP-RC beam specimens without shear reinforcement reported by 41 research groups. Furthermore, the accuracy of the proposed model was assessed through a comparative analysis with existing evaluation methods, encompassing machine learning-based models, empirical models, theoretical models, and design codes. The results indicate that the proposed model satisfactorily predicts the shear strength of FRP-RC beams within a wide range of design parameters. In comparison with machine learning-based models, the proposed theoretical model exhibits a similar level of accuracy in terms of the mean shear strength ratio and coefficient of determination (R2) values but with less scattering, indicated by lower coefficient of variation (COV) and root mean square error (RMSE) values. In addition, the proposed model outperforms existing empirical and theoretical models, as well as current design codes, by significantly enhancing prediction accuracy, demonstrated by lower COV, RMSE, and higher R2 values. Finally, a parametric study was conducted to investigate the effects of the key parameters on the shear strength of FRP-RC beams using both the proposed model and representative existing evaluation methods.

Evaluation of Rotation Capacity and Bauschinger Effect Coefficient of I-Shaped Beams Considering Loading Protocol Influences

Recent catastrophic earthquake events have reinforced the necessity of evaluating the seismic performance of buildings. Notably, the buildings can go into the plastic phase during a striking earthquake disaster. Under this condition, the current design codes assume seismic response reduction by virtue of the energy dissipation capacity of the structural members. In the strong-column–weak-beam design, which involves I-shaped beams and boxed columns, the mechanism is defined as a standard design scheme to prevent the building from collapsing. Therefore, energy dissipation relies highly on the I-shaped beam performance. However, the I-shaped beam performance can differ depending on the loading history experienced, whereas this effect is untouched in the prevailing evaluation equation. Hence, this study first performs cyclic loading tests of 11 specimens using different loading protocols. The experimental results clarify the fluctuation in the structural performance of I-shaped beams depending on the applied loading hysteresis, proving the necessity of considering the stress history for proper assessment. Furthermore, the database of experimental results is constructed based on the previous experimental studies. Ultimately, the novel evaluation equation is proposed to reflect the influences of the loading protocol. This equation is demonstrated to effectively assess the member performance retrieved from the experiment of 65 specimens, comprising 11 specimens from this investigation and 54 specimens from the database. The width–thickness ratio, shear span-to-depth ratio, and loading protocols are utilized as the evaluation parameters. Moreover, the prediction equation of the Bauschinger effect coefficient is newly established to convert the energy dissipation capacity under monotonically applied force into hysteretic energy dissipation under the cyclic forces.

Classification and ultimate capacity of duplex stainless steel H-section under cyclic loading

Stainless steel materials are high ductility and strain hardening under cyclic loading, which is promising in seismic design. However, the current European stainless steel structure design code prEN 1993-1-4(EC3) ignores this favorable effect in the cross-section classification, as well as the lack of prediction formulas for the ultimate capacity of H-section under cyclic loading. In this paper, parametric analysis was carried out for H-section to extend the database based on the existing test results after calibration of the finite element model. The cross-section classification criteria of duplex stainless steel beams and beam-columns around major-axis under cyclic loading were investigated, and the EC3 classification of stainless steel H-section was evaluated. The predicted results for EC3 are conservative due to not considering the constraints of the cross-section component plates and the favorable conditions for the material strengthening of stainless steel under cyclic loading. Based on this, classification criteria for stainless steel H-section under cyclic loading were proposed and summarized. Subsequently, the method of calculating the ultimate capacity methods under cyclic loading suggested by EC3, Chen and Zhou et al. were evaluated. The results show that EC3 is on the conservative side, with actual results being generally 1.5 times higher than the predictions. In contrast, Chen and Zhou et al.'s method is on the unsafe side of the prediction. Finally, improvement suggestions are given for EC3 and the continuous strength method by considering the over-strength factor under cyclic loading, respectively, with results exhibiting high accuracy.

Experimental investigations into stocky composite columns of concrete-filled circular S690 steel tubes under compression

Composite columns of concrete-filled steel tubes (CFSTs) are very efficient in providing large structural resistances and rigidities. However, high strength S690 steel tubes are not covered in current design codes. Therefore, a series of experimental investigations into stocky composite columns with circular CFSTs under compression were conducted. A total of 21 stocky composite columns with different tube diameters and thicknesses made of Grades S355, S460 and S690 steel and Grade C60/75 concrete were tested under different loading conditions. Moreover, extensive measurements on the surface strains of the steel tubes were made during tests. Data analyses on the test results reveal that all composite columns exhibit enhanced section resistances and ductility at large deformations, indicating that the use of S690 steel and C60/75 concrete in these composite columns are highly efficient. A simple method for determining confining pressures provided by the steel tubes to the concrete cores in these composite columns is proposed, which involves a systematic analysis on the measured data and the use of von Mises yielding criterion without any complicated plasticity formulation. Based on the proposed method, the resistance contributions of both the steel tubes and the concrete cores are successfully quantified. Comparison between the measured and the predicted resistances using EN 1994–1-1 of these composite columns reveals that while the section resistances of these composite columns are safely predicted, the resistances of the steel tubes are underpredicted while those of the concrete cores are overpredicted correspondingly. The findings highlight the need to improve the predictability of the current design rules, and to give increased resistances of the steel tubes when high strength S690 steel tubes are used.

A robustness-oriented procedure for the design of tying reinforcement in precast concrete hollow-core floors

Buildings may be subjected during their service life to extreme events which can trigger progressive collapse. On this front, the role played by tying reinforcement in structural members is crucial for an adequate load redistribution and the avoidance of disproportionate collapse. This work proposes a robustness-oriented procedure for the design of tying reinforcement placed in the hollow-core units and beams of precast concrete buildings, where limited studies are available in scientific literature. In particular, the aim is to provide a simple yet reliable approach for the design of concentrated and distributed ties in precast floors by adopting fundamental input parameters such as the system’s chord rotation capacity and dynamic amplification factor, which are not considered in current design codes. Firstly, a flow-chart of the design procedure is proposed and discussed. Secondly, the input parameters are calculated based on recent analytical approaches - proposed by some of the authors - to optimize the tying reinforcement design. Finally, the efficiency of the design procedure is demonstrated with an application example, and a novel detailing scheme is proposed which is aimed at a significant enhancement of structural robustness. Due to its simplicity, the proposed design procedure is contended to be applicable in robustness assessment and design of building structures with precast concrete hollow-core floors.

LIQUEFACTION-INDUCED DAMAGE IN THE CITIES OF ISKENDERUN AND GOLBASI AFTER THE 2023 TURKEY EARTHQUAKE

<p>On February 6th 2023 two major earthquakes struck southeast Turkey, M7.7 Kahramanmaras and M7.6 Elbistan, respectively. Unfortunately, due to the impact of these catastrophic events more than 50 000 casualties and 35 000 collapsed buildings have been reported since then. The aim of the study is to demonstrate preliminary site response analysis and assessment of re-liquefaction potential of sites which have been affected by the earthquakes – especially the cities of Iskenderun and Golbasi. Both site-specific areas have clear evidences of liquefaction and lateral spreading events which imply the focus of the presented paper. A series of geophysical MASW and microtremor tests have been performed in order to determine shear wave velocities up to depth of 30 m as well as the fundamental natural frequency of the soil deposits. </p> <p>Moreover, samples have been collected from sand and silt ejecta in order to evaluate some basic physical properties – grain-size curves, specific gravity and plasticity parameters. On the basis of the obtained data seismic classification of the investigated sites according to current design codes has been made and in-depth distance to relatively stiff layer has been assumed. For the sake of evaluating risk of re-liquefaction the widely-used simplified stress-based approach to triggering assessment has been adopted considering some rules of the thumb (e.g., sieve analysis and plasticity properties evaluation). Lastly, post-liquefaction reconsolidation settlement and lateral displacement have been determined in terms of future earthquakes</p>

Numerical Simulation of Polymeric Strap Material Reinforced Walls Under Seismic Excitation

This paper presents a comparison between the two-dimensional finite element and experimental results of shaking table tests on six one-third-scale polymeric strap or polymeric geostrip reinforced walls performed under seismic excitation at given peak ground accelerations [Formula: see text]. The effects of initial tangent stiffness or the stiffness of polymeric strap material [Formula: see text] and the slope angle of the cohesionless backfill material [Formula: see text] on the maximum relative displacement, [Formula: see text], of the reinforced earth wall, the values of the horizontal incremental dynamic earth pressure [Formula: see text] with distributions, acceleration responses, horizontal dynamic active earth pressure coefficient [Formula: see text] and maximum dynamic tensile forces [Formula: see text] were assessed in this study. Moreover, the vertical dynamic active earth pressure coefficients [Formula: see text] and the angles of the resulting dynamic active force with horizontal [Formula: see text] were predicted from the numerical analysis. Closely matched responses between the experimental and numerical studies were attained. Data obtained from experimental and numerical studies illustrated that increasing the slope angle of the cohesionless backfill material resulted in an increase in the values of horizontal displacement in the walls, and in dynamic earth pressure and root mean square acceleration [Formula: see text]. Increasing the stiffness of the reinforcement material caused a decrease in horizontal reinforced earth wall displacement and increases in dynamic earth pressure. In addition, the conventional pseudostatic limit equilibrium methods overestimated [Formula: see text] values, whereas they underestimated [Formula: see text] values, and the recommended [Formula: see text] values by current design codes were not found to be compatible with the numerical and experimental results.

Punching shear tests in flat slabs supported on re-entrant corner columns

The punching strength and deformation capacity of slab-column connections is governing for design at ultimate limit state of flat slabs. This phenomenon has been investigated since decades with experimental programmes in an effort to derive empirical or mechanical design approaches. Such efforts, due to the complexity of the phenomena, have mostly been addressed to axisymmetric inner slab-column connections, which correspond to the simplest academic case and are not directly covering a large variety of practical situations. Although some tests are also available for other configurations, such as edge or corner connections, no experimental evidence is found on relevant cases for practice such as re-entrant corner columns. The lack of experimental data in this latter case raises questions on the design of such connections, as extrapolating results from other cases is not a simple task due to the complexity of the phenomena implied (such as redistributions in the shear field and moment transfer between slab and column). In order to advance the knowledge on the response of re-entrant connections and to provide a sound design approach for them, this paper presents the results of an investigation specifically addressed at this case. To that aim, seven specimens were tested under different conditions, varying the load eccentricity, flexural reinforcement and shear reinforcement arrangement at the edges. The tests were instrumented with refined measurements, allowing to understand in a detailed manner the response of the slabs during testing in the shear-critical region. The experimental results are later compared to current design codes, leading to a number of conclusions with practical relevance. Finally, on the basis of the knowledge acquired from the tests, a mechanical approach is proposed based on the Critical Shear Crack Theory to assess the punching response. This approach is shown to lead to accurate and reliable predictions of the punching strength, improving those of current design codes.

Axial compression behavior and reliable design approach of rectangular dune sand concrete-filled steel tube stub columns

Concrete-filled steel tube (CFST) columns, incorporating various types of concrete, are increasingly prevalent in engineering applications. This study develops a finite element (FE) model and a design methodology for rectangular dune sand-concrete-filled steel tube (DS-CFST) columns. Investigating the composite behavior of rectangular DS-CFST columns and the effects of different DS replacement ratios, the results indicate a reduction in the ultimate bearing capacity compared to traditional CFST columns, attributed to diminished confinement effects, particularly at higher DS replacement ratios. Analysis of different design factors, including concrete and steel strengths, steel ratio, and aspect ratio, assesses their impacts on axial load-bearing capacity and composite behavior. This analysis leads to the establishment of a design formula, validated through experiments and FE analysis. The formula's efficacy and conciseness are evaluated against current design codes, with a reliability study assessing sensitivity to fluctuations. The proposed formula demonstrates accurate predictions of the ultimate load-bearing capacity.

Axial compressive stability design of longitudinal asymmetrical shuttle-shaped columns

Longitudinal asymmetrical shuttle-shaped column (LA-SSC) has found its wide application when subjected to combined axial compression and horizontal point load in practical engineering. This paper focuses on elastic and elasto-plastic buckling behaviors of the LA-SSC only under axial compression and the resulting outcome could provide an indispensable basis for further establishing buckling strength prediction of LA-SSC under axial compression and horizontal point load. At first, the elastic buckling behavior of tapered columns (TC) and longitudinal symmetrical shuttle-shaped columns (LS-SSC) are derived in theory and verified by finite element numerical results, and corresponding elastic buckling modes are discussed. Subsequently the elastic buckling load prediction of LA-SSCs is established first and the corresponding normalized slender ratio, as a key design parameter, is generalized. Finally, the stability capacity of LA-SSCs is involved in theoretical analysis and finite element (FE) numerical calculation under axial pressure. Through investigating the axial load-lateral displacement curves and axial stress distributions the buckled LA-SSCs, the effects of different parameters (such as overall length, plate thickness, and steel strength) on the axial compression stability capacity of LS-SSCs are explored. As a result, the complete design formulas for axial compression stability capacity of LA-SSCs are presented first and compared with current major design codes in various countries. It is observed that the proposed strength design formulas are in good correspondence with the FE numerical results. The proposed formulas could provide references and guidance for the axial compression buckling strength of LA-SSCs under axial compression and they further supply fundamentals for establishing the strength design recommendation of LA-SSCs under axial compression and bending moments.

EVALUATION OF SEISMIC FORCES ACCORDING TO EUROCODE 8 AND SNiP II-7-81. COMPARATIVE ANALYSIS

The evaluation of seismic forces is very important for the design of all types of structures. In the present, Republic of Moldova is in a period of transition in the construction industry from the national design norms to the European design norms. The comparison provides an interesting and imperative approach in design of structures. During the design process it is very important to be aware of all the forces acting on a structure, especially the accidental forces. This paper presents a comprehensive analysis of a concrete frame structure, subjected to seismic action. A calculation is performed according to the current national design code SNiP II-7-81 and according to Eurocode 8. The purpose of the paper is the quantitative comparison of the values of the seismic forces and the qualitative evaluation of the factors that influence these forces.

Understanding the multi-source uncertainties effect on the seismic performance assessment of deeply hydraulic tunnels based on the generalized PDEM

One crucial element of a seismic performance evaluation approach is to appropriately account for the stochastic characteristics of SGMs and the uncertainty associated with material properties. Furthermore, the incidence angle of seismic waves may be influenced by topographic and geological factors, leading to uncertainty and randomness. This variability in incident angles has the potential to cause unforeseen structural damage. However, the current seismic design code of underground structures has commonly assumed the vertical or horizontal seismic input method in underground engineering. From the uncertain point of view, the multi-source uncertainties that incorporate the nonstationary SMGs, seismic input angles, and material parameters utilized to conduct the seismic performance assessment of HTs remain a challenge in current seismic design and performance evaluation. To overcome this challenge, the Generalized F-discrepancy method, the generalized PDEM, and the equivalent extreme-value event are introduced to conduct stochastic dynamic analysis and develop the appropriate fragility curves of HTs considering the multi-source uncertainties. The results demonstrate that the probability of damage of the HT obtained by multi-source uncertainties is significantly different in analyzing the single uncertain and two uncertainties. Moreover, it can be concluded that the multi-source uncertainties can cause more seismic demand than the single uncertain and two uncertainties under different earthquake intensity levels for the HT. In light of this, it is strongly suggested that seismic design and performance assessment of HTs take into account the relevant aspects, such as the input angles, the random features of seismic waves, and the material parameters.

A Corrosion- and Repair-Based Reliability Framework for Offshore Platforms

Offshore platforms are important infrastructures that often face severe environmental conditions, such as corrosion, throughout their lifetime. This can continuously decrease their structural robustness. Despite the availability of many anti-corrosion strategies, there is still a need for a sound management scheme that can systematically address the lifetime operation of offshore platforms under corrosion. To address this, the work here proposes a corrosion- and repair-based reliability framework for the lifetime operation of offshore platforms. A fixed offshore platform is designed based on current design codes for severe environmental conditions in a given return period, and the effect of corrosion on the structure’s serviceability is modeled. The results show that the extent of the corrosion depth and damage in different years highly affects the ability of a repair to restore a damaged element to its original design strength. The results also show that the residual reliability of the structural members under the splash zone becomes almost zero after the first 10 years of the operation period, implying that these members require quick repair strategies. This study establishes a management program for fixed offshore platforms subjected to long-term corrosion by performing reliability analyses on the components of the platforms and evaluating the maintenance of the components in the splash zone. In the absence of commonly accepted contemporary industry practice standards, this study proposes a corrosion growth model based on API-RP-2A, DNV, and NORSOK standards that can effectively evaluate code-based structural designs. The framework developed here can help offshore platform owners in their decision-making process for corrosion-based safety analysis.

Experimental axial-compressive behaviour of bare cold-formed-steel studs with semirigid-track and ideal-hinged boundary-conditions

Studs are the primary load-bearing components in cold-formed steel (CFS) wall panels, connected to tracks at both ends with self-tapping screws, forming a semirigid boundary condition (BCT). Most existing tests on the axial compressive behaviour of bare CFS studs are based on either theoretically-hinged (BCH) or fully-fixed boundary conditions. Previous researchers have employed BCT only on sheathed stud-wall panels. However, practicing engineers and current design codes, e.g., Eurocode 3, follow an all-steel design. Therefore, this research experimentally investigated bare-CFS-studs' axial compressive behaviour with BCT, considering, for the first time, the combined effect of the tracks' warping rigidity, stud-to-track gap, non-linear connection stiffness, and bare studs' various cross-sectional slenderness. Forty-two industry-standard lipped channel sections (studs) of five thicknesses (1.2-3 mm), three depths (75–125 mm), and two heights (1.2 & 1.5 m) were tested under static-concentric axial compressive loading with BCT. Another fourteen studs were tested with BCH, a comparator to BCT. Results demonstrated that the studs' global failure mechanisms were flexural-torsional in BCT instead of flexural in BCH. Studs' axial stiffness was two-phased in BCT due to the stud-to-track gap, compared to single-phased stiffness in BCH. >1.8 mm stud-to-track gap caused stud-to-track connections' failure and studs' sudden capacity reduction during gap closure. Studs achieved 1.22 times higher axial-compressive strength, 2.3 times more axial-shortening, 0.7 times lower axial stiffness, and 58% lower axial-compressive strain at the web-midheight under BCT-PhaseII than BCH. Tested strengths were compared with EC3 design strength, and an effective-length-factor of 0.65 was suggested for efficient design of studs with BCT.

Comparative Analysis of Shear Strength Prediction Models for Reinforced Concrete Slab–Column Connections

This research focuses on a comprehensive comparative analysis of shear strength prediction in slab–column connections, integrating machine learning, design codes, and finite element analysis (FEA). The existing empirical models lack the influencing parameters that decrease their prediction accuracy. In this paper, current design codes of American Concrete Institute 318-19 (ACI 318-19) and Eurocode 2 (EC2), as well as innovative approaches like the compressive force path method and machine learning models are employed to predict the punching shear strength using a comprehensive database of 610 samples. The database consists of seven key parameters including slab depth (ds), column dimension (cs), shear span ratio (av/d), yield strength of longitudinal steel (fy), longitudinal reinforcement ratio (ρl), ultimate load-carrying capacity (Vu), and concrete compressive strength (fc). Compared with the design codes and other machine learning models, the particle swarm optimization-based feedforward neural network (PSOFNN) performed the best predictions. PSOFNN predicted the punching shear of flat slab with maximum accuracy with R2 value of 99.37% and least MSE and MAE values of 0.0275% and 1.214%, respectively. The findings of the study are validated through FEA of slabs to confirm experimental results and machine learning predictions that showed excellent agreement with PSOFNN predictions. The research also provides insight into the application of metaheuristic models along with ANN, revealing that not all metaheuristic models can outperform ANN as usually perceived. The study also highlights superior predictive capabilities of EC2 over ACI 318-19 for punching shear values.

Post-earthquake fire resistance of self-centering concrete beam-column joint: An experimental investigation

Fire is an accidental disaster resulting in disastrous consequences for building. Post-earthquake fire is a secondary disaster induced by earthquake, triggering off larger destruction in a higher probability of occurrence. The potential severity of consequences to structures makes fire and post-earthquake fire safety imperative in the design of any new structures. Self-centering concrete joints are introduced as a promoting alternative to traditional reinforced concrete (RC) joints. They always exhibit excellent seismic performance and self-centering capacity, available in high-seismic zone. However, the current lack of experimental data on fire response of self-centering concrete joints means that they remain an open issue in current design codes. In this paper, full-scale quasi-static cyclic test and fire tests were conducted on two self-centering concrete joints connected with bolted angles and posttensioned (PT) tendons. The experiments aimed to explore the performance of self-centering joint in fire situations, and the impact of post-earthquake damages on fire response of self-centering joint. The deformation patterns and thermal responses of self-centering joints including temperature distribution, prestress force of PT tendons, displacements at beam ends and duration were recorded and analyzed. The results show that both self-centering joints exhibited satisfactory fire resistance with endurance over 170 min. Generally, the bolted angles and PT tendons in self-centering concrete joints showed acceptable working performance in fire. The findings unveil the actual response of self-centering concrete joints during the fire and post-earthquake fire conditions, providing experimental data for further numerical simulation and analysis. It can be used to calibrate the design approach for self-centering joints under fire and seismic-induced fire exposure.

Investigating climate change effects on bridges and tunnels

The earth's climate is changing, partly from continued natural warming since the last ice age and partly man made. The changing climate with resulting more extreme weather events is likely to impact bridges and other long-life infrastructure assets. This research considers the broad effects of climate change on load effects, load combinations and material properties of bridges and tunnels. Effects such as temperature, fire, storminess, precipitation, snow, ice, wind, sea levels and acidity as they affect bridges are discussed. The uncertainty of the data in its probability and the magnitude of extreme events on these climate effects is noted and discussed in relation to resilience. Specific examples of where climate change may affect bridges and tunnels are considered, and where further research is required. A risk assessment of the likelihood and impact of climate change is presented to quantify the effects on bridges and tunnels, to support design or asset management decisions. The work is primarily based on British and north European data, but data from other parts of the world are also considered. Current code and standard provisions for design and assessment are reviewed in relation to climate change and resilience, and recommendations are outlined. Conducting asset- or region-specific risk assessments using the methods of this research is recommended.

Driven pile foundation reuse in East London, UK

Multiple phases of redevelopment of the London Docklands, UK, have resulted in the need to replace existing structures with new, often larger, structures. This paper presents the case history of a 1980s low-rise office building (three to four storeys) being replaced by a medium-rise (five storeys + roof terrace) recreational building structure. The 1980s building was founded on driven closed-ended steel tube piles located within one of London’s historic docks. Subsequent to the 1980s building construction, London Underground (LU) tunnels were constructed below the dock in the late 1990s in close proximity to the structure. Piling in the dock adjacent to the LU tunnels resulted in restrictions to pile construction methodology. The new structure reused the driven piles in the dock and added new onshore bored piles to accommodate a larger building footprint landwards. The pile reuse justification used the original preliminary pile load test and driving records along with current design codes. The 1980s allowable working loads stated on the design drawing were lower than that required to support the new building, thereby requiring reinterpretation of preliminary pile load test results. The pile reuse assessment justified an increase in pile working load from 1050 to 1760 kN.

Optimum Strut-and-Tie Models for Reinforced Concrete Beams

In this study, the authors suggested three optimum strut-and-tie models (STMs), which consider all reinforced concrete (RC) beams' failure behavior characteristics. The recommended models are valid for the RC beams with a shear span ratio (a/d) of less than 4.5. For each model, the authors also proposed a force distribution ratio, described by the portion of force carried by a truss mechanism, to assist structural designers in conducting the appropriate design using the current design codes' STM methods. In determining the force distribution ratios, the authors incorporated the influences of the main design variables, such as the a/d ratio, flexural rebar ratio, and concrete strength. The authors verified the appropriateness of the suggested STMs and force distribution ratios by using them for the strength verification of 758 RC beams tested to failure. The proposed STMs and force distribution ratios predicted the RC beams' failure strength quite well. The average test-to-predicted strength ratios (and coefficient of variations) by the present study and conventional STM models of design codes were 1.07 (21.3%) and 1.75 – 1.82 (27.6 – 45.7%), respectively.