Moment Demands Research Articles

Numerical and analytical study of pinned column base plate connections

Gravity system column base plate connections are generally classified as pinned connections with no to minimal moment capacities. A low rotational stiffness value is recommended by the New Zealand Steel Structures Standard, NZS 3404, to represent pinned connections. However, numerous past research studies have shown that these so-call pinned connections possess significant rotational stiffness which could attract large moment demand and potentially lead to yielding of the column base. Furthermore, the constant axial load on the gravity column in conjunction with column base yielding could result in axial shortening of the column, which would significantly increase the cost and difficulty of post-earthquake rehabilitation. With the aim to minimize column base yielding and column axial shortening, a numerical parametric study was conducted to examine the influences of various parameters, including base plate thickness, anchor rod diameter, axial load magnitude, foundation depth and anchor rod pitch distance, on the connection behaviour. It was found that the applied axial load greatly affected the moment resistance as well as the rotational stiffness of the connection. Results also showed that the rotational stiffness of pinned column base plate connections was significantly higher than the value suggested in NZS 3404. An analytical model was developed and validated against numerical and experimental studies to predict moment-rotation response of pinned column base plate connections. Satisfactory results were observed.

Time-Dependent Seismic Reliability of Coastal Bridge Piers Subjected to Nonuniform Corrosion.

Coastal bridge piers suffer random performance deterioration owing to the presence of complex nonuniform corrosion characteristics and material uncertainties. Some of these piers will also be threatened by random earthquakes during a long-term service period, and therefore, structural safety needs to be probabilistically assessed by the seismic reliability method. To deal with this problem, we present a method to calculate the time-dependent reliability of the coastal bridge pier, comprehensively considering the randomness of a seismic event, nonuniform corrosion, and material uncertainty. First, the time-dependent M-N interaction diagrams are established by using the Monte Carlo simulation method. On the basis of the interaction diagrams, the moment resistance reduction function and time-dependent moment resistance distribution are determined. Subsequently, the moment demand under the seismic load is determined using the Poisson model and the response acceleration spectrum. Then, the formulas to calculate the time-dependent reliability of a nonuniform corroded pier are derived on the basis of the theorem of total probability. The proposed method is illustrated with a case study of a coastal bridge pier. It was found that the increase in corrosion damage would obviously increase time-dependent reliability. Furthermore, the increase in submerged zone height delayed the year when the failure section shifts from the pier bottom to the bottom of the splash and tidal zone, and it reduces the failure probability of the coastal pier. The research results presented herein show that the nonuniform corrosion manifestations influence the failure mode-related time-dependent seismic reliability of the coastal bridge pier.

Seismic performance of self-centering hybrid coupled wall systems: Preliminary assessments

Hybrid Coupled Wall (HCW) systems consist of reinforced concrete walls connected with steel coupling beams. HCWs benefit from the superior lateral stiffness of the reinforced concrete walls, while the coupling mechanism reduces the moment demand at the base of the walls. The present study investigates the seismic performance of a new HCW system equipped with friction-damped self-centering coupling beams and examines the efficiency of the new system in reducing residual deformations. The coupling beams of the intended HCW system consist of self-centering links, which can be easily repaired after severe earthquake events. The self-centering system utilized in this study features the following advantages distinguish it from conventional self-centering solutions: (i) it eliminates the coupling beams elongation problem (ii) it facilitates the application of pre-fabricated self-centering components to mitigate uncertainties raised by post-tensioning the connections on site. In this paper, the seismic behavior of the proposed lateral load-bearing system is investigated under several ground motion records and intensities. It is demonstrated that the applied self-centering mechanism has the capacity to minimize earthquake-induced residual deformations and repair time without increasing the damage level expected for the concrete walls in conventional HCWs.

Energy dissipation estimation of steel slit shear panel dampers with tapered links considering the effect of out-of-plane buckling

The steel slit shear panel (SSSP) with tapered links is one type of efficient energy-dissipating devices, with tapered shape of the links accommodating the bending moment demand when subjected to lateral shear deformation. To dissipate the maximum amount of seismic energy, full plasticity is expected to be developed. However, out-of-plane buckling, which is almost inevitable for thin plates, significantly reduces its energy dissipation capacity. This work aims to quantify the amount of energy dissipation of SSSPs with tapered links considering the effect of out-of-plane buckling. Quasi-static cyclic loading tests on five SSSP specimens with different design parameters are conducted, based on which the refined numerical model is built and validated. In estimating the energy dissipation, the effect of out-of-plane buckling needs to be considered. Otherwise, the estimated energy dissipation can be as much as over two times the tested value. To consider the effect of out-of-plane buckling, the index of average pinching parameter is adopted. A new method is derived for estimating the energy dissipation of SSSPs with considering the effect of out-of-plane buckling, feasibility of which is validated using the obtained test results.

Out-of-plane flexural behaviour tests and numerical analysis of LEM-infilled CFS walls

With carbon neutrality gradually becoming the global focus, employing the energy-saving wall in structure has become the development trend of energy-efficient buildings. This paper focuses on a novel type of cold-formed steel (CFS) wall in which lightweight expanded polystyrene (EPS) mortars (LEM) are filled in the space of CFS framing. The CFS framing and LEM are formed into a whole to resist the bending moment demands. To explore the flexural response of the LEM-infilled CFS wall, six specimens were designed and tested. These specimens included two specimens without wall sheathing and four specimens sheathed with various panel types. The specimens were subjected to gradually increased uniformly distributed loads. Failure patterns, load–deflection relationships, capacities and strain distribution of typical points were also analyzed. Test results illustrated that the flexural bearing capacities of the specimens were 9.69–13.14 times their self-weight. Specimens with sheathings exhibited better flexural response, and specimens with cement-based LEM exhibited higher flexural stiffness and capacities than that of specimens with gypsum-based LEM. Subsequently, finite element (FE) models of LEM-infilled CFS walls were developed and validated by the test data. Effects of steel yield strength, steel thickness, LEM compressive strength and wall panel type on the flexural behaviours of LEM-infilled CFS walls were explored by parametric studies. The transformed cross-section method was employed to calculate the mid-span deflection and the results were validated by test and FE analytical results. The analysis in this research could provide reasonable references for design and application.

Learning to love ourselves again: Organizing Filipinx/a/o scholar-activists as antiracist public health praxis.

A critical component for health equity lies in the inclusion of structurally excluded voices, such as Filipina/x/o Americans (FilAms). Because filam invisibility is normalized, denaturalizing these conditions requires reimagining power relations regarding whose experiences are documented, whose perspectives are legitimized, and whose strategies are supported. in this community case study, we describe our efforts to organize a multidisciplinary, multigenerational, community-driven collaboration for FilAm community wellness. Catalyzed by the disproportionate burden of deaths among FilAm healthcare workers at the onset of the COVID-19 pandemic and the accompanying silence from mainstream public health leaders, we formed the Filipinx/a/o Community Health Association (FilCHA). FilCHA is a counterspace where students, faculty, clinicians, and community leaders across the nation could collectively organize to resist our erasure. By building a virtual, intellectual community that centers our voices, FilCHA shifts power through partnerships in which people who directly experience the conditions that cause inequities have leadership roles and avenues to share their perspectives. We used Pinayism to guide our study of FilCHA, not just for the current crisis State-side, but through a multigenerational, transnational understanding of what knowledges have been taken from us and our ancestors. By naming our collective pain, building a counterspace for love of the community, and generating reflections for our communities, we work toward shared liberation. Harnessing the collective power of researchers as truth seekers and organizers as community builders in affirming spaces for holistic community wellbeing is love in action. This moment demands that we explicitly name love as essential to antiracist public health praxis.

A comparative study on structural design alternatives for twisted tall buildings with outriggers

Tall buildings are seen as iconic landmarks because of their bold effect on the city silhouette. To control this bold effect in an aesthetically desired manner, designers search for intriguing forms such as twisted buildings. There are two main approaches for designing the structural system of a twisted tall building. In the first approach, the twisted form of the building is obtained only by the rotation of the floors, and the structural system is maintained in a conventional, perpendicular way. Alternatively, the structural system and the floors of the building twist together. This study designates these as non-adaptive and adaptive, respectively. With different heights and angles of twist, non-adaptive and adaptive tall building models are created and analysed under the combined effect of wind and gravity loads. The dynamic properties, drift, moment, and torsion demands are compared to scrutinize and assess the potentials and limitations of these alternative approaches.

Exacerbating patellofemoral pain alters trunk and lower limb coordination patterns and hip-knee mechanics

The exacerbation of patellofemoral pain (PFP) may lead to compensatory trunk and lower limb movement patterns in order to minimize patellofemoral joint loading. However, joint kinematics are often analysed in isolation, which limits the understanding of how the underlying segments were coordinated to produce limb postures and distribute load across the limb. In this study we used a dynamical systems approach to investigate how women with PFP coordinate trunk, hip, and knee motion and distribute hip-knee moment demands following symptom exacerbation. Coordination patterns and coordination variability of the trunk, hip, and knee from 61 women with PFP were obtained during stair descent, ascent, and step down tasks, before and after a pain exacerbation protocol. Hip-knee extensor moment impulse ratio was also calculated. Following the exacerbation of PFP, women utilized knee dominant coordination patterns less often (p = 0.039–0.027; d = 0.51–0.53), while coordination patterns with the trunk leaning forward were utilized more during stair negotiation (p = 0.043-<0.001; d = 0.52–0.96). Although no significant differences in hip-knee coordination patterns were found, there was an increase in the hip-knee impulse ratio during stair negotiation (p = 0.014-<0.001; d = 0.27–0.36). These findings seem to display a movement strategy utilized by women with PFP in order to distribute more load to the hip joint and less to the knee joint, possibly in an attempt to avoid/manage pain.

Comparative fire-following-earthquake performance of code-compliant low-rise base-isolated structures

Seismic base isolation is an effective way of protecting structures against seismic loads and is very effective in terms of both collapse mitigation of structures and protection of non-structural elements under severe ground shaking. In this study, the structural demand of base-isolated three- and four-story steel moment-resisting frames is determined in case of a fire event followed by an earthquake, and compared with the results of fixed-base frames, which have similar geometry, load, and seismic hazard for a location in California. Four compartments are selected as possible locations for fire events in each building, and beams and columns in those compartments are exposed to a representative temperature increase in time, which includes a cooling phase as well. Maximum, minimum, and residual axial force, and moment demands on elements of the fire compartments, and drift demand of structural frames on the first and second floor, where the fire is assumed to occur, are determined and compared. Results are given in terms of parameters of three-parameter log-normal distribution, hence fragility curves can be constructed for each response considered in the study. Seismic isolation is effective in reducing both maximum and residual drift demand of the frames, and axial force in the beam element for each compartment considered. Fixed-base frames have 20% more maximum axial load on beams. Beam and column elements in the four-story configuration are under relatively more moments in case of a fire, while the performance of three-story frames depends on the location of the assumed fire.

Non-Iterative Optimal Design Method Based on LM Index for Steel Double-Beam Floor Systems Reinforced with Concrete Panels.

Steel double-beam floor systems reinforced with concrete panels can improve the structural and environmental performance of buildings by reducing moment demands and embodied CO2 emissions. However, for steel double-beam floor systems, a time-consuming iterative analysis is required to derive an optimal design proposal owing to the rotational constraints in the composite joints between the concrete panel and steel beams. In this study, a non-iterative optimal design method using the LM index is proposed to minimize the embodied CO2 emissions of steel double-beam floor systems. The LM index is a measure that can be used to select the optimal cross-section of the steel beams considering the decreased moment capacity according to the unbraced length. The structural feasibility of the proposed design method was verified by investigating whether safety-related constraints were satisfied by the LM index with respect to the design variables under various gravity loads. The applicability of the proposed optimal design method is verified by comparing the embodied CO2 emissions derived from the proposed and code-based design methods. Applicable design conditions were presented based on the LM index to aid engineers. The proposed design method can provide environmentally-optimized design proposals to ensure structural safety by directly selecting the LM index of steel beams.

Seismic performance of high-rise dual modular wall-frame systems

Hinged walls (HWs) were frequently used to control lateral deformation profiles of moment-resisting frames (MRFs) under earthquakes. In high-rise hinged wall-frame systems, the seismic moment demand and required stiffness of the walls are too large that it is difficult for the walls to stay in elastic range and making the MRF deform uniformly under major earthquakes. To reduce the seismic moment demands applied on the wall, this paper proposed a modular hinged wall with buckling-restrained braces to strengthen MRFs and convert the MRFs to a dual system (MHWBBF). The modular hinged walls are composed of different number of modular HW segments with/without buckling-restrained braces (BRBs) and used to form various study cases. Nonlinear time history analyses using 10 ground motions considering two intensity levels were performed for the purpose of investigating the seismic performance of different study cases. The results indicate that the proposed MHWBBF works as expected, which is mainly because: (1) the usage of modular HW segments can significantly reduce the seismic force demands on the walls; (2) the usage of BRBs can effectively reduce the structural displacement responses and inter-story drift differences among different HW segments.

Optimized Interaction P-M diagram for Rectangular Reinforced Concrete Column based on Artificial Neural Networks Abstract

ABSTRACT This study proposes an artificial neural network for a design of reinforced concrete (RC) columns for structural engineers who are interested in performing reverse designs, exploring influences of structural parameters (e.g., , and ) or code requirements on structural performances. The proposed networks enable both forward and reverse designs for an RC column, which is challenging to be achieved using conventional designs. An AI-based surrogate model of RC columns with sufficient training accuracy can comprehensively replace conventional design software, exhibiting excellent productivity for both forward and reverse designs. In addition, useful reverse design models based on neural networks can be established by relocating preferable control parameters, including safety factor (SF = ) and an aspect ratio of column sections, into the input region. All associated design parameters, including , , and , are computed on an output side. Design charts, such as the P–M diagram, are constructed, demonstrating design moment strength equal to the factored moment demand by specifying SF = 1. The design scenarios can be extended as further as possible to meet the requirements of engineers.

Influence of foundation damping on offshore wind turbine monopile design loads

The dynamic behavior of offshore wind turbines (OWTs) must be designed considering stochastic load amplitudes and frequencies from waves and mechanical loads associated with the spinning rotor during power production. The proximity of the OWT natural frequency to excitation frequencies combined with low damping necessitates a thorough analysis of sources of damping; of these sources of damping, least is known about the contributions of damping from soil-structure interaction (foundation damping). This paper studies the influence of foundation damping on cyclic load demand for monopile-supported OWTs considering the design situations of power production, emergency shutdown, and parked conditions. The NREL 5 MW Reference Turbine was modeled using the aero-hydro-elastic software FAST and included equivalent linear foundation stiffness and damping matrices. These matrices were determined using an iterative approach with FAST mudline loads as input to a soil-pile finite element software which calculates hysteretic material damping. Accounting for foundation damping in time history analysis can reduce cyclic foundation moment demand by as much as 30% during parked conditions, 25–33% during emergency shutdown, but only 2–3% reduction during power production without wave and wind misalignment. The calculated foundation damping from the emergency shutdown cases agreed with experimental testing performed in similar site conditions.

A Semi-Active Control Technique through MR Fluid Dampers for Seismic Protection of Single-Story RC Precast Buildings.

The work proposes an innovative solution for the reduction of seismic effects on precast reinforced concrete (RC) structures. It is a semi-active control system based on the use of magnetorheological dampers. The special base restraint is remotely and automatically controlled according to a control algorithm, which modifies the dissipative capability of the structure as a function of an instantaneous dynamic response. The aim is that of reducing the base bending moment demand without a significant increase in the top displacement response. A procedure for the optimal calibration of the parameters involved in the control logic is also proposed. Non-linear modelling of a case-study structure has been performed in the OpenSees environment, also involving the specific detailing of a novel variable base restraint. Non-linear time history analyses against natural earthquakes allowed testing of the optimization procedure for the control algorithm parameters, finally the capability of the proposed technology to mitigate seismic risk of new or existing one-story precast RC structures is highlighted.

Effects of vertical ground acceleration on the seismic moment demand of bridge superstructure connections

Vertical ground accelerations are not always considered in bridge design practice, which is partially due to the lack of consistent recommendations in the design codes and standards. However, undeniably, the vertical ground acceleration component in an earthquake can be large. While the effects of vertical ground acceleration on bridges have been studied in the past, the focus has mostly been on performance of the substructure, especially columns. This study thus investigates the effects of large magnitude of vertical ground accelerations on the response of bridge superstructures as it can experience significant impact, particularly in the connections and bearing forces. To quantify the effects of vertical ground accelerations and compare the outcomes with existing design recommendations, an analytical study is undertaken on the seismic response of straight, skewed, and curved steel bridge superstructures with drop pier caps. The results show that the vertical accelerations can amplify the superstructure moment demands at the midspan and support locations by as much as above 100%. It is further shown that the current design practice to account for vertical ground acceleration effect is not sufficient for earthquakes with high vertical ground accelerations. Although the superstructure used in this study incorporated steel girders, the results are also applicable to bridges with concrete superstructure.

‘Do You Hear Voices, or Do You Think You Hear Voices?’: Malevolence and Modernity in the Psychiatric Clinic

Based upon fieldwork at India’s National Institute of Mental Health and Neurosciences (NIMHANS), I trace the contours of hysteria as an enduring, albeit informal, analytic that continues to disturb neuropsychiatric reductionism within psychiatry. I argue that at this historical moment, the political and economic demand for singular identities out of more porous cultural life-worlds (e.g. ethnic, religious, linguistic, occupational) produces clinical subjects incapable of nuance and flexibility, hastening a host of possessive, literalist, legalist and ‘hysteric’ symptoms that overtake India’s most vulnerable modern subjects, fuelling the sense of a crisis in search of a pharmaceutical solution to a psychopathological diagnosis.

Determination of optimal behavior of self-centering multiple-rocking walls subjected to far-field and near-field ground motions

In recent years, innovative seismic resistant systems have been introduced based on the Damage Avoidance Design (DAD) philosophy rather than the conventional plastic design-based methods to reduce damages to buildings and to decrease post-earthquake repair costs. Self-centering multiple-rocking walls are amongst these innovative systems. This study aims to determine the optimum number of rocking sections in self-centering concrete multiple rocking walls. To this aim, the seismic behavior of self-centering (SC) concrete rocking walls of 8, 12, 16, and 20 stories with different numbers of rocking sections were examined. Several non-linear time-history analyses were carried out via OpenSEES software in a two-¬dimensional framework. Three sets of ground motions were considered including 22 Far-Field (FF), 14 Near-Field-Pulse (NFP), and 14 Near-Field-no Pulse (NFnP). Five types of quad-rocking walls and one type of dual-rocking walls were specified and compared with base-rocking walls and fixed-base walls. To perform this comparison, a set of utility coefficients was defined to integrate different response aspects including shear and moment demands as well as the residual drifts. The results showed that the effects of higher modes (shear and moment demand) increase with the increase in the height of the rocking structures. Furthermore, NFnP and FF records produced higher mode effects in rocking systems as compared to NFP records. The results suggested that the quad-rocking walls with the reduced tendon area in the first block (R4-S1) are highly effective in reducing the effects of higher modes in NFP and NFnP records. They showed maximum utility coefficients of 67% and 65%, respectively. Also, quad-rocking walls with the reduced tendon area in the third block (R4-S3) were more effective under FF records and their maximum utility coefficient was 65%. The residual roof drift of rocking walls was so negligible that its maximum value in the 8-story structure under NFP records was 0.0008.

EFFECT OF ANCHORAGE REBARS APPLYING TO MID-STORY PIN COLUMN BASE CONNECTION ON STRESS TRANSFER MECHANISM AND ULTIMATE SHEAR STRENGTH UNDER HORIZONTAL FORCE

Mid-story pin column system has been proposed to realize beam yielding mechanism of a steel moment-resisting frame. In this system, a pin connection system is applied inbetween the upper steel column and the lower RC column extended from the base beam to control moment demands on both ends of the first story column. An exposed-type column base has been adopted as a pin connection connected by a single anchor bolt. Static cyclic horizontal loading tests of a partial frame consisting of the first story column and the second floor beams showed a frame with the proposed column base system exhibited stable hysteresis performance up to a story drift angle of 0.05 rad, remaining column in elastic. In addition, the RC column with the connection of a single anchor bolt exhibited slippage at the connection while this problem was solved when an anchor bolt was stiffened by cross-shaped four shear plates. A cover plate was also welded on the top of the shear plates to cover the top surface of the RC column from bearing pressure of the upper steel column. An anchor bolt with the welded plates are called an anchor bolt set, or ABS, hereinafter. Ensuring a reliable seismic performance of an upper steel frame, damages at the proposed connection have to be minimized. So far, compressive stress transfer mechanism was clarified, and the ultimate compressive strength of the connection was evaluated in the previous study.

Effect of Base-Level Inerters on the Higher Mode Response of Uplifting Structures

Allowing slender structures to uplift has been used as an efficient means of controlling their seismic response. Oftentimes rocking structures will exhibit some degree of flexibility and cannot be adequately represented by single-mass or rigid systems. In this paper, we examine the dynamic response of multistory flexible rocking bodies equipped with inerters at their ground level. First, numerical models of inerter-equipped rocking structures are formulated and validated. These models are used to assess the effect of the inerter on the elastic deformations and base rotations demands of a set of structures ranging from 3 to 9 stories. Importantly, we examine the interaction between impact forces and higher vibration modes and evaluate the effectiveness of the inerter in controlling the associated acceleration demands and increased bending moments along the height. The efficiency of the inerter was not found to be affected by practical variations of the stiffness of the rocking surface. Although the inerter increased the moment demands at the first level, the proposed strategy successfully controlled seismic demands along the height of the structure.

Structural behavior prediction of the Butterfly-shaped and straight shear fuses

Structural fuses can be implemented in buildings as steel plates subjected to shear loading. Strategically engineered cut-outs in these steel plates can be used to create shear fuses with energy dissipating capability. The structural fuses are used to protect the surrounding structure from damages and significant inelastic deformations, and then be replaceable after a major earthquakes. Previous studies indicate that structural fuses with shear fuses improve the initial elastic stiffness, energy dissipation capability, and ductility of structures.Butterfly-shaped fuses with varying width between larger ends and a smaller middle section have been used to better align bending capacity with the moment demand along the length of the fuse. These fuses have been shown in previous tests to be capable of substantial ductility and energy dissipation. In this study, equations are developed to capture load–displacement behavior of butterfly-shaped and straight shear fuses. The butterfly angle, defined as the angle between intersections of the inclined edges at the middle of the fuse, is investigated. Using the flexural and shear limit state equations, the critical butterfly angle identifying the transition from the shear to flexure is proposed. Subsequently, equations describing the geometric hardening of butterfly-shaped shear fuses are proposed. Along the same lines, the stiffness of a typical butterfly-shaped fuse is developed by dividing the stiffness into four major parts: fuse flexural deformations, fuse shear deformations, and shear and flexure deformations of the end zones. In addition, the post-yielding hardening behavior is investigated considering axial forces generated under shear loading deformations.Subsequently, computational finite element models are presented and validated with laboratory tests for two different configuration examples to examine the implementation of the proposed limit state prediction. To verify the provided applicability of the proposed analytical equations, a set of computational models are considered, and the associated backbone behavior of the models are compared with their corresponding proposed equations. The procedures presented in this paper to predict the behavior of fuses could be useful for the design of butterfly-shaped fuses with more than 90% accuracy in predicting the backbone behavior of the fuse system.