Simplified Design Approaches Research Articles

The upper bound of the buckling stress of axially compressed carbon steel circular cylindrical shells

Abstract The buckling stress of axially compressed circular cylindrical shells (CCSs) is highly sensitive to imperfections. The literature proved that it is hard to generalize the imperfections and the designers are encouraged by the Eurocode EN 1993:1-6 (2007) to conduct geometric and material nonlinear with imperfections analysis (GMNIA) considering different possible forms of imperfections for the shell under design. As GMNIA type of analysis is difficult and requires highly skilled engineers, knowledge of the upper limit of the buckling stress serves as a guide and prevents the overestimation of the shell buckling resistance. It also encourages average skill designers to attempt GMNIA as far as the maximum possible limit is known. Thus, the objective of this study is to provide the upper bound of the buckling stress of carbon steel CCSs. Geometric and material nonlinear analysis (GMNA) of perfect circular cylindrical shells for a wide range of R/t ratio is conducted. It has been found that for cases of small and intermediate R/t values the buckling stress can be predicted by GMNA while the elastic buckling controls those of larger R/t values. The limiting R/t values depend on the steel grade and have been derived for the available standard grades of carbon steel. The obtained results are presented in terms of simplified formulas and a design chart to be used by engineers. Application of the proposed upper bound in simplified design approaches using knock down factor (KDFs) has also been discussed.

Numerical Study of Thermal Efficiency in Light-Gauge Steel Panels Designed with Varying Insulation Ratios

In the construction domain, there is a growing emphasis on sustainability, resource efficiency, and energy optimisation. Light-gauge steel panels (LGSPs) stand out for their inherent advantages including lightweight construction and energy efficiency. However, the effective management of thermal efficiency, particularly addressing thermal bridges, is crucial. This paper conducts a detailed numerical investigation into the thermal performance of LGSPs, examining varied insulation ratios. Thermal finite element (FE) models were initially developed using the THERM software and validated against code predictions and results available in the literature. A comprehensive parametric study explored different insulation ratios, insulation materials, and wall thicknesses, discovering their impact on thermal transmittance (U-value). Key findings revealed that U-value correlated with insulation material conductivity, with E-PLA insulation exhibiting the lowest values, and increasing wall thickness resulted in decreased U-values. It was found that a strategic use of insulation yielded a U-value reduction of over 65%. New simplified design approaches were developed, featuring insulation ratios linked to accurate U-value predictions for LGSP configurations. The new design approaches were found to provide more accurate and consistent U-value predictions. Moreover, optimum insulation ratios for new builds and existing building extensions were found to be around 0.9 and 0.7 for 275 mm and 325 mm thick walls, respectively. These proposed energy-efficient solutions, facilitated through advanced design, are well-aligned with net-zero construction objectives.

Numerical Simulations and Simplified Design Approaches for Large-Rupture-Strain FRP-Strengthened Reinforced Concrete Beams under Impact

Numerical Simulations and Simplified Design Approaches for Large-Rupture-Strain FRP-Strengthened Reinforced Concrete Beams under Impact

On a numerical methodology to assess the fatigue life of connecting rods

Although simulation-based fatigue analysis is a standard tool adopted in every sector including automotive industry, the design of engine components in automotive and motorsport applications mostly relies on simplified design approaches supported by time-consuming testing programs. This manuscript proposes a new methodology based on individual engine speed damage estimation and engine speed time history combined with Palmgren-Miner linear damage rule to predict the fatigue state of the connecting rod. The track data, engine multibody simulation (AVL ExciteTM) and engine combustion simulation (AVL BoostTM) are used to generate the initial variable trace that is processed to obtain the block programs. Stress amplitude estimated with finite element analysis (Abaqus) are used to estimate the damage from S-N curve and the cumulative damage is estimated with Palmgren-Miner cumulative damage model. The method proposed is demonstrated using a connecting rod case study and the duty cycle from the race on Sebring international raceway. This work shows the suitability of the approach and the benefit in terms of accuracy in the prediction of the fatigue life.

Inverse analysis-based model for the tensile behaviour of fibre-reinforced concrete with manufactured and waste tyres recovered fibres

The urgency of finding green solutions within the construction industry encouraged, in latest years, the adoption of sustainable materials for structural concrete. One of the most up-and-coming proposal is the use of recycled steel fibres, to complement or possibly replace traditional steel reinforcement. Nevertheless, the contribution of the fibres on the mechanical performance of concrete is still uncertain and requires further investigation. This study is aimed at providing an analytical model for the tensile response of concrete reinforced with manufactured steel fibres and recycled steel fibres recovered from waste tyres. The proposed model features several parameters ruling the cracking strength, the post cracking behaviour and the residual tensile strength of fibre-reinforced concrete. The parameters in the analytical model were calibrated by numerical simulation of toughness tests on specimens with different types and contents of fibres in the mixture. A satisfactory simulation of experimental load-crack tip opening displacement curves was obtained, with numerical-vs-experimental curve scatter lower than 10%. However, the variability of experimental results hindered obtaining an accurate blind simulation of additional tests selected from the literature. On the other hand, a clear correlation between the parameters ruling the cracking strength-to-residual strength ratio and fibres amount was identified for both recycled and manufactured fibres. The outcome of this study showed that the proposed model can be used in simplified design approaches, to account for the fibres’ type and content in the evaluation of tensile response of fibre reinforced concrete.

Simplified design approaches for panel zones in steel special moment frame buildings

Panel zones (PZs) can be proportioned to be weak, balanced or strong. Damage to steel special moment frames (SMFs) in past earthquakes has highlighted the limitations of weak PZ design, leading to its discontinuation from design practice. Balanced and strong PZ approaches remained acceptable, but the shear demand and capacity for which PZs need to be proportioned to achieve a balanced or strong PZ still remain ambiguous. In this work, three different PZ design approaches were investigated (named PZ-I, PZ-II and PZ-III) by incorporating them in seismic design of selected study buildings. The shearing behaviour of the PZs was evaluated using the results of non-linear analyses, which indicated that PZ-I, PZ-II and PZ-III led to weak, balanced and strong PZ behaviour, respectively. In particular, PZ-I design was found to lead to excessive shearing distortions in the PZ. Thus, in order to either limit or entirely eliminate inelasticity in the PZs of steel SMF buildings, it is appropriate to adopt PZ-II or PZ-III design. It is recommended that adopting the PZ-II design approach would suffice for moment frame buildings in regions of moderate seismicity.

Assessment and design considerations for single layer cylindrical lattice shells subjected to seismic loading

This paper examines the main considerations related to the seismic design and assessment of single layer steel cylindrical lattice shells, and offers recommendations for their practical application. Geometric configurations covering a wide range of rise to span ratios are considered within the investigation. An insight into the relative influence of seismic loading on shell design, in comparison to gravity conditions, is firstly provided through the use of digital parametric engineering procedures. This is followed by linear elastic response assessments which are used to propose a simplified procedure for estimating the internal seismic forces for the purpose of member sizing in early design stages. Suitable approaches for pushover analysis are then discussed and used to identify inherent plastic mechanisms. The results of incremental nonlinear dynamic analysis, using a suite of fourteen records, are also employed in order to validate the findings and to further assess the ultimate response under realistic seismic loading conditions. Based on the findings, representative ranges for behaviour factors and displacement modification coefficients are derived alongside discussions on their implementation within codified seismic design procedures. Apart from providing recommendations for simplified design approaches, the assessments presented in this paper can also be used to support detailed performance based guidelines as well as for informing geometry and size optimisation strategies.

Correlation of Concurrent Extreme Metocean Hazards Considering Seasonality

Simultaneous occurrence of metocean variables can present a multihazard to maritime systems. However, simplified design approaches to assess simultaneous significant wave heights and wind velocities are lacking, especially if seasonality is considered. This is addressed in this study by using extreme significant wave heights and companion wind velocities recorded in the Gulf of Mexico. Time-dependent, generalized extreme value (GEV) models and classical regression are the basis to propose a simplified approach to estimate correlated extreme significant wave heights and wind velocities associated with given return periods, accounting for seasonality and including measures of uncertainty. It is found that the proposed approach is a new but simple method to adequately characterize the concurrent extreme metocean variables and their uncertainty. It is concluded that the method is an effective probabilistic design tool to determine simultaneous extreme significant wave heights and companion wind velocities for desired return periods and seasonality.

Seismic performance of single layer steel cylindrical lattice shells

This paper examines the elastic and inelastic seismic behaviour of single layer steel cylindrical lattice shells. The main dynamic characteristics for this form of structure are firstly examined through a parametric assessment, which also leads to proposed expressions for estimating the fundamental period and mode of vibration. The seismic response of five typical shell configurations, representing a wide range of rise to span ratios, is then assessed within the linear elastic range under selected earthquake excitations. Particular focus is given to the relative influence of the horizontal and vertical seismic components on the internal actions. In order to provide a means for evaluating the underlying inelastic behaviour, a simple pushover approach, which is suitable for this structural form, is suggested using the forces obtained from the fundamental mode shape. The peak angle change is proposed as a damage parameter within the nonlinear analysis for characterising the inelastic global and local demands in shells of different geometries. Incremental dynamic analysis is subsequently carried out in order to evaluate the detailed nonlinear time history response. The results provide detailed insights into the influence of the horizontal and vertical excitations on the nonlinear seismic response, and illustrate the suitability of the peak angle change as an inelastic deformation measure for shells of different geometric configurations. The main findings from the linear and nonlinear assessments are highlighted within the discussions, with a view to providing guidance for performance based assessment procedures as well as simplified design approaches.

Pile groups under axial loading: an appraisal of simplified non-linear prediction models

The settlement behaviour of vertically loaded pile groups has been the subject of an extensive body of research over the past two decades. In particular, this work has identified the over-conservatism associated with predictions of pile interaction derived from elastic theory and the corresponding amplification of group settlement relative to single pile values. Researchers have since redoubled efforts to refine settlement predictions for pile groups towards more economical design, largely through more rigorous treatment of soil stiffness non-linearity. Although foundation design engineers are increasingly employing three-dimensional continuum analyses to quantify pile interaction on a site-specific basis, simplified design approaches remain an integral part of preliminary foundation design. The purpose of this paper is to undertake a critical examination of these methods with a view to increasing their potential for take-up by foundation engineering practitioners. A database of simplified models has been collated for the prediction of non-linear pile interaction that exists within vertically loaded pile groups. These models are categorised as either analytical or empirical. The development, limitations and range of applicability of these models are explored in detail in the context of some published case histories.

Bending behavior of cement-based multi-layered roof elements

The two major earthquakes occurred in Northern Italy in 2012 (magnitude 6.1 and 5.8) shown that a serious debate over the structural safety of existing industrial buildings is utterly necessary, also in regions traditionally considered less exposed to the seismic hazard. A promising retrofitting strategy may be represented by the substitution of inefficient secondary roof components with innovative lightweight panels, capable of simultaneously ensuring a global reduction of the inertial forces and an increase of the building energy performances. In this paper, the structural behavior of a multilayered solution, consisting of an advanced cement-based case enclosing a thick insulating core, is presented and investigated on real-scale specimens. The mechanical characterization of the employed materials (High-Performance Fiber Reinforced Cementitious Composite and Textile Reinforced Concrete) at the laboratory level is followed by the discussion of the major challenges arisen in transferring such sensitive construction technologies to the prototyping plant. Structural performances are evaluated by means of longitudinal and transverse bending tests and simplified plane-section design approaches are finally explored and critically assessed.

Shear strength of RC beams subjected to axial load

Due to the complex mechanism of the shear failure, most shear design equations in codes and guidelines are based on empirical approaches and consequently should only be used within the bounds of the test population from which they were developed. To accommodate this issue, a mechanics-based segmental approach, which can simulate a reinforced concrete (RC) beam with any type of concrete and reinforcement and which can explain the physical process of shear failure has been proposed to determine the shear capacity of RC beams with and without stirrups. In this paper, this segmental approach is extended by incorporating axial load in the mechanics-based model; furthermore, a closed form solution for assessment is also derived. By simulating 61 published test specimens, the proposed approaches are validated with good correlation between the predicted and measured strengths. Being mechanics based, this approach has a great potential to be developed for all types of RC structures with all combinations of loading for use in the development of or refinement of simplified design approaches.

State of the Art on Basic Methodologies for Crashworthy Design of Automotive Body Components Considering Axial Collapse Mode

The body structure of a passenger vehicle is one of the important functional groups of a vehicle. A crashworthy car body structure is so conceptualised as to absorb considerable amount of the impact energy by deforming in definite areas, and thereby reduce the deceleration experienced by its passengers to survivable levels. The non-deforming areas of the car body structure are designed as stiff survivable space for the passengers. Various criteria, such as deformation pattern, deceleration pulse of the vehicle, different bio-mechanical criteria defined for the passengers etc., can be used for assessing the crashworthiness of vehicles. Various methods have been developed and used over the years to analyse and optimise the crashworthiness of vehicles. This paper presents an overview of simplified design approaches for analysing car body components for their behaviour in crash events. This includes a brief summary of various collapse modes. Main characteristics of the axial collapse mode and simplified design approaches available for this mode, relevant for our research work, are also presented.

State of the Art on Basic Methodologies for Crashworthy Design of Automotive Body Components Considering Bending Collapse Mode

The body structure of a passenger vehicle is one of the important functional groups of a vehicle. A crashworthy car body structure is so conceptualised as to absorb considerable amount of the impact energy by deforming in definite areas, and thereby reduce the deceleration experienced by its passengers to survivable levels. The non-deforming areas of the car body structure are designed as stiff survivable space for the passengers. Various criteria, such as deformation pattern, deceleration pulse of the vehicle, different bio-mechanical criteria defined for the passengers etc., can be used for assessing the crashworthiness of vehicles. Various methods have been developed and used over the years to analyse and optimise the crashworthiness of vehicles. This paper presents an overview of simplified design approaches for analysing car body components for their behaviour in crash events. This includes a brief summary of various collapse modes. Main characteristics of the bending collapse mode and simplified design approaches available for this mode, relevant for our research work, are also presented.

Performance assessment and optimization of fluid viscous dampers through life-cycle cost criteria and comparison to alternative design approaches

The performance assessment and optimal design of fluid viscous dampers through life-cycle cost criteria is discussed in this paper. A probabilistic, simulation-based framework is described for estimating the life-cycle cost and a stochastic search approach is developed to support an efficient optimization under different design scenarios (corresponding to different seismicity characteristics). Earthquake losses are estimated using an assembly-based vulnerability approach utilizing the nonlinear dynamic response of the structure whereas a point source stochastic ground motion model, extended here to address near-fault pulse effects, is adopted to describe the seismic hazard. Stochastic simulation is utilized for estimation of all the necessary probabilistic quantities, and for reducing the computational burden a surrogate modeling methodology is integrated within the framework. Two simplified design approaches are also examined, the first considering the optimization of the stationary response, utilizing statistical linearization to address nonlinear damper characteristics, and the second adopting an equivalent lateral force procedure that defines a targeted damping ratio for the structure. These designs are compared against the optimal life-cycle cost one, whereas a compatible comparison is facilitated by establishing an appropriate connection between the seismic input required for the simplified designs and the probabilistic earthquake hazard model. As an illustrative example, the retrofitting of a three-story reinforced concrete office building with nonlinear dampers is considered.

Understanding sampling disturbance and behaviour of structured clays through constitutive modelling

The effects of sampling disturbance on structured clays with initial states above the oedometric Intrinsic Compression Line (ICLoe) are investigated numerically by applying a modified form of the Ideal Sampling Approach (ISA) and an elasto-viscoplastic constitutive model. The main features of the behaviour of structured clays during and after sampling reported in the technical literature can be replicated. Notwithstanding the inevitable damage to the microstructure of the “nominally undisturbed” specimens, the reconsolidation procedures commonly applied in laboratory practice are confirmed to be beneficial, even where they are not conceptually justified, as is the case of the SHANSEP approach. While it is possible to determine the strength and compressibility of “ideal” specimens from numerical interpretation of laboratory tests on “nominally undisturbed” specimens, the problems related to their direct use in conventional simplified design approaches for stability and settlement predictions are highlighted.

Retrofitting of RC Frames by Steel Braced Frames Utilizing a Hybrid Connection Technique

This study presents a new connection technique to retrofit existing RC frames by steel braced frames. The proposed connection which is called the “hybrid connection” plays two important structural roles. The first role is to provide connection between an existing RC frame and a steel braced frame. The second role is to increase shear strength and axial compression capacity of boundary RC columns of retrofitted frames. The hybrid connection consists of steel plates, high-strength bolts, and high-strength grout. Experimental investigations were conducted on four one-bay one-story RC frames and one one-bay two-story RC frame which were retrofitted by the proposed method. Moreover, one one-bay one-story RC frame was tested as a non-retrofitted benchmark frame. Experimental results of the specimens indicated that the proposed hybrid connection transferred relatively high direct shear forces between the RC frames and the installed steel braced frames to obtain lateral capacity of the steel braces. In addition, the proposed hybrid connection prevented possible shear failure of the boundary RC columns with the help of the utilized steel plates. Taking into consideration experimental results and observations, simplified design approaches are presented to estimate lateral strength of fundamental failure mechanisms of retrofitted RC frames.

Parametric Studies and Preliminary Design Recommendations on the Use of Postinstalled Shear Connectors for Strengthening Noncomposite Steel Bridges

This paper is a continuation of research on strengthening the load-carrying capacity of existing noncomposite bridge girders by postinstalling shear connectors. In this study, finite element models were developed to evaluate the behavior of composite beams retrofitted with postinstalled shear connectors over a wide range of variables with an objective of providing preliminary design recommendations. Variables considered in the parametric studies included beam depth, span length, and shear-connection ratio. The parametric studies showed that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders strengthened using postinstalled shear connectors. Use of a shear-connection ratio of less than 30% is not recommended to avoid nonductile behavior of the strengthened girder.

Experimental Behavior of Bridge Beams Retrofitted with Postinstalled Shear Connectors

A number of older bridges were constructed with floor systems consisting of a noncomposite concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders with postinstalled shear connectors to permit the development of composite action. This paper presents the results of an experimental investigation of this concept. Five large-scale noncomposite beams were constructed, and four of these were retrofitted with postinstalled shear connectors and tested under static load. The retrofitted composite beams were designed as partially composite with a 30% shear connection ratio. A noncomposite beam was also tested as a baseline specimen. Test results showed that the strength and stiffness of existing noncomposite bridge girders can be increased significantly. Further, excellent ductility of the strengthened partially composite girders was achieved by placing the postinstalled shear connectors near zero-moment regions to reduce slip demand on the connectors. The test results also showed that current simplified design approaches commonly used for partially composite beams in buildings provide good predictions of the strength and stiffness of partially composite bridge girders strengthened using postinstalled shear connectors.

Some Issues in Seismic Analysis and Design of Blockwork Wharves

During past decades, a number of ports worldwide have suffered extensive earthquake-related damage. As seaports play a key role in the world's economy, their seismic performance should be enhanced, clearly stated and reliably pursued by designers. This work focuses on seismic vulnerability of wharves in Italy. According to a recently carried out statistical study, most of the existing wharves are gravity-type, made of superimposed, dry-connected blocks, particularly in older facilities. Such technology is widely in use worldwide but it has not attracted much research interest so far. In the present study, the validity of current, simplified design approaches has been investigated by comparison with the results of inelastic dynamic time-history analyses. Permanent displacements of the wall blocks have been calculated. Available performance criteria have been reviewed. A real wharf structure in the Port of Ancona (Italy) has been studied in depth, as a methodological example. For such structure, a parametric study has been conducted with the aim of investigating the role played by different design parameters and to assess the validity of the widely in use pseudo-static method.