Column strength requirements in multi-storey seismic frames

Recent vibration serviceability problems of many structures have drawn researchers' attention to the walking-induced vibration modelling and assessment of floors and footbridges. Stochastic nature of human-induced vibration and its dependency on numerous conditions significantly reduce the accuracy of the current non-stochastic design procedures and consequently the level of confidence on them. This paper tends to study the performance of two of the most recent design guidelines, UK National Annex to Eurocode 1 (2008) [1] and French Sétra guideline (2006) [2], on real structures and to highlight their advantages and disadvantages. These methods are used to calculate dynamic reactions of a slender and lightly damped pre-stressed concrete slab strip and an as-built footbridge using various loading scenarios such as group loading, spatially unrestricted flow of pedestrians, and crowd loading. The calculated structural responses under first and second harmonics of walking load are further compared with their corresponding experimentally acquired reactions to examine their accuracy and efficiency. Various potential sources of discrepancy in the results of these procedures in comparison with the experimental data, such as missing human-structure interaction effects (e.g. damping), invalid 'perfect periodicity' assumption, limited applicability and unrealistic people correlation are then discussed. Finally the effects of using stationary pedestrians' added damping on performance of considered design models are investigated and briefly discussed. The results of this analysis can provide a comprehensive insight into current design procedures' accuracy and shall be taken as a good starting point for future researches in this area.

To extend previous research on obtaining designs that rely on a second-order inelastic hinge analysis to demonstrate that a structure is adequate in resisting the effects of factored loads, this paper presents a study of a series of two-story planar steel frames where all columns are subjected to combinations of axial force and minor-axis bending. Inelastic designs, which are prepared to satisfy both strength and serviceability limit states requirements, are compared to designs obtained using a conventional second-order elastic analysis in conjunction with the AISC LRFD Specification. The degree of accuracy and reliability of using a concentrated plasticity analysis to model system behavior is also established. The study indicates that for a majority of the frames investigated, a second-order inelastic hinge analysis can be used effectively to design steel structures. It is also shown that in some cases a distributed plasticity analysis may be required.

This paper assesses the reliability of code-compliant linear and nonlinear dynamic analyses for irregular buildings with base isolation system (BIS). Comprehensive analyses are carried out for a case study comprising a large reinforced concrete multi-storey framed hospital with 327 high-damping rubber bearings. Spectral and time history (linear and nonlinear) analyses were performed on the three-dimensional (3D) finite element model (FEM) of the structure; simplified analyses were also conducted on single-degree-of-freedom (SDOF) systems. It is found that, at damageability limit state, the values of maximum interstorey drifts (d/h) computed with spectral analyses on the three-dimensional FEM range between 1/6 and 1/10 of the code limit (d/h = 0.33%); thus more stringent code limits should be required for buildings with BISs. The maximum floor acceleration is reduced by about 70% with respect to the ground acceleration (free field site); the acceleration profile is uniform along the height of the multi-storey frame. Threshold values of floor accelerations to assess the seismic performance of equipments in buildings with BIS are lacking. At ultimate limit state (ULS), spectral analyses provide values of actions and deformations that are less conservative than those derived through time history analyses. To perform reliable dynamic analyses of base isolated buildings it is crucial to select natural earthquake ground motions compliant with the fundamental period of vibration of the structural system. Nevertheless, it is not straightforward to select adequate natural strong motions in the catalogues available world-wide; buildings incorporating BISs possess periods of vibration which are generally higher than 2.0 s. As a result, distant and high-magnitude earthquakes are effective for base isolated buildings; nevertheless, such earthquakes are scarce in the seismic databases. The outcomes of the present study also demonstrate that simplified linear analyses tend to provide estimates of the response quantities, displacements of base isolators and base shear of the superstructure, which can be reliably employed at preliminary design stage. Spectral analysis results of the 3D model tend to match those of the SDOF systems, even for irregular superstructure, provided that modal mass participating ratios are greater than 85–90%. The results of spectral analyses on both SDOF and three-dimensional FEM envelope the outcomes of linear time histories.

The maneuverability and compactness of small-wheel and folding bicycles are greatly appreciated. Nonetheless, the performance of these small-wheel bicycles as compared to the big-wheel bicycles has always been questioned. They are often blamed for being less stable, wobbly, or twitchy. It is still unclear how the performance of the small-wheel bicycle designs can be improved. Both small- and big-wheel bicycles are designed with similar ergonomics; therefore, the focus has been on the front steering design. The steering design parameters of 91 big-wheel and 27 small-wheel bicycles were compared, bearing in mind the available front steering design guidelines to understand: (1) the influence of big-wheel bicycle’s frame design on small-wheel bicycles and (2) most common range of design parameters used in current bicycle designs. The analysis showed a strong influence of current big-wheel bicycle design practice on front frame parameter selection of small-wheel bicycles. Furthermore, the self-stability comparison over the most common design range confirmed the lesser stability in the current small-wheel bicycle designs at normal riding speed. However, it was also found that the lesser stability was not the result of small wheels per se, but rather owing to an inadequacy in the current design approach to addressing the complex influence of reducing wheel size and bicycle frame design on its stability and performance. Therefore, an improved design methodology was adopted by incorporating the bicycle dynamics into the current design approach and the front steering design guidelines for small-wheel bicycles have been developed. The guidelines contradict the current small-wheel bicycle design practice, as they recommend steeper headtube angles for small-wheel bicycles. The guidelines were validated with good agreement between the theoretical and experimental results on two prototype 20-inch-wheel bicycles having counter-intuitive steering geometry.

There has been constant deliberation regarding promising seismic performance enhancement techniques for the reinforced concrete (RC) high-rise structures built before adopting existing seismic design codes. The research reported in this paper focuses on advanced approaches for improving the seismic performance of the shear wall structural system using high-performance reinforced concrete jackets and an outrigger-bracing system consisting of braces with improved hysteresis response. Following the case study region’s seismicity and design criteria, inelastic analyses are conducted to evaluate the demand-to-capacity ratios of primary vertical structural members of a pre-code twenty-six-story building. With the application of the proposed retrofit approaches and their various configurations, the design inadequacy of several structural members is eradicated. After validating the adopted fiber-based discretizations of the retrofit techniques with recent experimental studies, detailed three-dimensional numerical models are developed for the high-rise structures. Inelastic pushover analyses and dynamic response simulations under a diverse set of earthquake ground motions with increasing intensity levels are conducted to capture the buildings’ seismic performance until failure. The probabilistic seismic performance assessment enabled selecting the most effective technique for enhancing the seismic performance of shear wall buildings while minimizing disruption to the building.

This work focused on modeling the transient thermal behavior of objects on the surface of the Moon. We determined the impact of the lunar environment, such as latitude, craters, boulders, and slopes, on the core temperatures of specific objects. In particular, we investigated a human in an EVA-suit, an exploration rover, and a highly integrated spacecraft. Internal parameters affecting the core temperature of the investigated objects are: body density, heat capacity, insulation, and internal power load level. The lunar geometry was modeled with the Thermal Moon Simulator (TherMoS) tool and the simulations were carried out with ESATAN-TMS. TherMoS is a tool currently under development to fill the gap in dynamic modeling of the thermal behavior of moving bodies on the lunar surface. The specific objects were modeled as generic spacecrafts without active thermal control. This model approach emphasizes temperature fluctuations at the expense of realism. The results of the semi-dynamic approach used in this paper, for non-actively controlled spacecraft, show that latitude and craters have the highest impact on sample body core temperatures (ΔT from 0 to -100 K, and +30 to -65 K, respectively, between undisturbed case and obstructed case), followed by boulders and nearby slopes (ΔT delta temperatures of +15 to -55 K and +20 to -45 K, respectively). Internal thermal loads have a significant impact as well, especially in the case of astronauts in space-suits. Temperature differences caused by the environment are most pronounced in rovers with small thermal inertia. Compared to static calculations, the semi-dynamic approach used in this work allows for the calculation of temperature gradients. For the case of a human in an EVA-suit, the calculated core temperature rate of change varied in the range of -0.041 to +0.045 K·min 1 . From these values, the heat flux necessary to maintain a core temperature of 310 K ranged from -178 W (required power for heating) to +196 W (excess heat, to be removed). Based on these findings we discuss the limits of current static and semi-dynamic thermal design approaches and simulation tools with regard to transient effects in the border zone between sunlight and shaded regions.

Hydraulic tracer studies in a pilot scale subsurface flow constructed wetland

Soil nailing is being used in many projects in glacial tills in Ireland, particularly to provide temporary support to steep slopes. Little design guidance is available for such materials, and it is known that the application of design procedures developed for other material is conservative. Detailed nail instrumentation and field monitoring has been undertaken during large-scale soil nailing works for the Dublin Port Tunnel project. It was found that the short-term behaviour of nails was the reverse of that assumed in current design methods. Most of the load was induced as a results of drilling and nailing the lift immediately below the nail being monitored rather than due to excavation-induced stress relief. The highest forces were developed in the upper nails where the largest ground movements occurred. This is the reverse of most current design methods where the highest soil–nail bond is assigned to the deepest nails. It seems that the observed short-term, prefailure behaviour of nailed slopes is governed more by the deformation pattern of the slope than by large-scale development of failed wedges. Current design procedures should be reviewed. Despite this, the trial confirmed that the currently used procedures are highly conservative for Dublin glacial till.

This paper investigates the development and optimization of artificial reefs through a new generative design method that integrates Computational Fluid Dynamics (CFD) with Bi-directional Evolutionary Structural Optimization (BESO). Since the 1950s, artificial reefs have been deployed to enhance marine ecosystems, and this study begins with a survey of existing reef designs. In response to limitations in current design approaches, we adopt a topology optimization strategy aimed at improving spatial allocation for polyphony expansion within reef structures. By coupling fluid-dynamic analysis with an iterative optimization loop, we evaluate the effectiveness of material exchange enabled by these artificial formations—an essential consideration given advanced manufacturing constraints and the need for rapid production of natural-like geometries. To extend artificial reef design into new possibilities, we propose a generative workflow in which reef morphology emerges from the interaction between CFD and BESO, iteratively removing and adding material in accordance with external loading conditions. The resulting reef is then compared with representative benchmarks from current artificial reef designs to assess material efficiency, structural performance, and geometric characteristics under complex underwater conditions.

Steel plate shear walls consist of thin infill steel plates attached to beams, called (horizontal boundary elements, HBEs), and columns (vertical boundary elements, VBEs) in structural steel frames. The thin unstiffened web plates are expected to buckle in shear at low load levels and develop tension field action, providing ductility and energy dissipation through tension yielding of the web plate. HBEs are designed for stiffness and strength requirements and are expected to anchor the tension field formation in the web plates. VBEs are designed for yielding of web plates and plastic hinge formation at the ends of the HBEs. This design approach may result in very large demand on boundary frame members, especially VBEs in most cases. Several methods such as using LYP, perforating the infill plate and omitting connection of infill plate to columns have been proposed to reduce the moment and axial force demands on the VBEs. Study the behavior of steel plate shear walls omitting the connection of infill plate and columns is the main purpose of this research. A classic analysis base on PFI method along with quasi static cyclic experimental study has been performed in order to investigate the behavior of such a system. The results of the experimental study are used to verify numerical models. Behaviors of proposed system (overall capacity and initial stiffness) were compared with those of the conventional SPSWs. Results show that both parameters are reduced in comparison to the conventional SPSWs.

One of the critical issues drawing attention of structural engineers is the reduction of post-event damage for multi-story buildings in seismic regions after earthquake excitation. Addressing this important concern helps to save lives and reduce building repair costs in the aftermath of a seismic event. One of the methods to address this issue utilizes structural systems or materials that have high elastic and plastic deformation capacity. The main objective of this paper is to investigate the seismic damage response of multi-story frame buildings with floors constructed using lightweight concrete and beams reinforced with glass-fiber reinforcement polymer (GFRP). A software of inelastic damage analysis of structures (IDARC) has been used to investigate the damage behaviour of 4 twelve-story frame buildings with lightweight concrete floors and glass-fiber reinforced beams and 1 reference traditional frame under three earthquake time-history excitations i.e. very severe, severe, and moderate intensity. Utilizing this lightweight concrete for floor construction which has specific weight as half as of traditional concrete will reduce the P–Δ effect. The high elastic deformation capacity of beams reinforced with GFRPs that have no plastic deformation, will absorb a large portion of kinetic energy produced by ground motion and consequently, will reduce the post-seismic damage.

Optimum definition of equivalent non-linear SDF system in pushover procedure of multistory r/c frames

E-scooters are a recent trend and are viewed as a sustainable solution to ease the first and last mile problem in modern transportation. However, an alarming rate of accidents, injuries, and fatalities have caused a significant setback for e-scooters. Many preventive measures and legislation have been put on the e-scooters, but the number of accidents and injuries has not reduced considerably. In this paper, the current design approach of e-scooters has been analyzed, and the most common range of design parameters have been identified. Thereafter, validated mathematical models have been used to quantify the performance of e-scooters and relate them with the safety aspects. Both standing and seated riders on e-scooters have been considered, and their influence on the dynamic performance has been analyzed and compared with the standard 26-in wheel reference safety bicycle. With more than 80% of the accidents and injuries occurring from falling or colliding with obstacles, this paper tries to correlate the dynamics of uncontrolled single-track vehicles with the safety performance of e-scooters. The self-stability, handling, and braking effect have been considered as major performance matrices. The analysis has shown that the current e-scooter designs are not as stable as the reference safety bicycle. Moreover, these e-scooters have been found unstable within the most common range of legislated riding velocity. The results corroborate with the general perception that the current designs of e-scooters are less stable, easy to lose control, twitchy, or wobbly to ride. Furthermore, the standing posture of the rider on the e-scooter has been found dangerous while braking to avoid any disturbances such as potholes or obstacles. Finally, the front steering design guidelines have been proposed to help modify the current design of e-scooters to improve the dynamic performance, hence the safety of the e-scooter riders and the surroundings.

This paper provides a state-of-the-art review on advanced analysis models for investigating the load-displacement and ultimate load behaviour of steel and composite frames subjected to static gravity and lateral loads. Various inelastic analysis models for steel and composite members are reviewed. Composite beams under positive and negative moments are analysed using a moment-curvature relationship which captures the effects of concrete cracking and steel yielding along the members length. Beam-to-column connections are modeled using rotational spring. Building core walls are modeled using thin-walled element. Finally, the nonlinear behaviour of a complete multi-storey building frame consisting of a centre core-wall and the perimeter frames for lateral-load resistance is investigated. The performance of the total building system is evaluated in term of its serviceability and ultimate limit states.

Column base is one of the most important element of steel structures. It is important to investigate the influence of elasto-plastic behavior of column bases on the ultimate earthquake resistance of steel frames. In this paper, a series of inelastic response analysis of multi-story steel frames with exposed type column bases, especially weak anchor bolt type column bases, were carried out. From the analytical results, following conclusions were obtained. 1)The intensity of the damage concentration at the structural element of the 1st story in the frames with exposed type column bases were much less than that of the frames with pin type column bases and the frames with fixed column bases. 2)Ultimate earthquake resistance of the frames with exposed type column bases were similar to that of the frames with pin type column bases. 3)If columns of the frames were ductile, ultimate earthquake resistance of the frames with exposed type column bases were similar to or a little better than that of the frames with fixed column bases. If columns of the frames were not ductile, ultimate earthquake resistance of the frames with exposed type column bases were much better than that of the frames with fixed column bases. 4)Energy absorbing capacity of the exposed type column bases were much less than other structural elements.