Gravity Frames Research Articles

Topology of charged AdS black hole in restricted phase space* *Supported by the National Natural Science Foundation of China (12075143, 12375050), and the Natural Science Foundation of Shanxi Province, China (202203021221209, 202303021211180)

The local topological properties of black hole systems can be expressed through winding numbers as defects. To date, AdS black hole thermodynamics are often depicted by the dual parameters of in the extended phase space, while there have been several studies on the black hole thermodynamics in the restricted phase space. In this paper, we analyze the topological properties of charged AdS black holes in the restricted phase space under the higher-dimension and higher-order curvature gravity frame. The results show that the topological number of the charged black hole in the same canonical ensembles is a constant and is independent of the concrete dual thermodynamical parameters. However, the topological number in the grand canonical ensemble is different from that in the canonical ensemble for the same black hole system. Furthermore, these results are independent of dimension d and highest order k of the Lanczos-Lovelock densities.

Cyclic moment-rotation model for bolted double-angle connections with composite floor systems

This paper presents a simplified moment-rotation model for cyclic response of bolted double-angle beam-to-column connections in composite steel frames with concrete on metal decking floors. The proposed model employs mechanics-based equations to determine model parameters, along with empirical observations from previous studies and data from recent large-scale multi-bay frame experiments. Several design variables and construction details, such as orientation of the metal decking, concrete reinforcement layout, and deck splicing details around the connection, were considered in the proposed model. Comparisons between the connection model and experimental results showed reasonable agreement in moment-resisting capacity up to 8% interstory drift. Notably, the proposed model adequately simulated varying responses based on connection details not captured by existing moment-rotation models. Analyses of 2- and 4-story frames using the proposed model showed up to 1.3 times higher ductility and 47% lower initial rotational stiffness compared to those using the existing ASCE 41 connection models with strengths of 20% and 35% of the plastic moment capacity of the girder. These results indicate the potential overestimation of stiffness and moment-resisting capacity, and the underestimation of ductility when using existing moment-rotation models due to insufficient modeling parameters to represent actual behavior. Therefore, the proposed model demonstrates its applicability in incorporating various design variables and construction details of bolted double-angle connections with composite concrete on metal deck floors. This model can be used to account for the non-negligible strength and stiffness of bolted double-angle connections in steel gravity framing under seismic loads.

Biaxial seismic response of base-column connections in sub-standard steel buildings: dataset.

Existing steel frames not complying with modern seismic codes are often vulnerable to earthquakes due to inadequate seismic detailing. These types of framed structures typically feature semi-rigid and partial strength column-base connections; the behaviour of such connections may significantly affect their seismic performance. However, current code provisions offer limited guidance for the assessment and retrofit of column-base connections To fill the knowledge gap, the H2020 EU-funded Earthquake Assessment of Base-Column Connections in Existing Steel Frames (HITBASE) project experimentally investigated, the response of exposed column-base plate connections. Bi-directional Pseudo-Dynamic tests were carried out at the Structures Laboratory (STRULAB) of the University of Patras within the framework of Engineering Research Infrastructures for European Synergies (ERIES). The case-study steel frame featured two types of column-base plate connections, i.e., stiffened and unstiffened, representing respectively the base connections of an external moment-resisting frame and an internal gravity frame. The experimental programme comprised free vibration tests to identify the modal properties of the sample steel frame. A set of quasi-static cyclic tests and Pseudo-Dynamic tests were then carried out to investigate the performance of the steel frame under bi-directional earthquake sequences. The response of each component constituting the column-base plate connections was monitored during the tests to fully capture the behaviour of the connections. Such experimental results allow model calibration and further parametric investigation on column base plate connections.

Distributed set-membership estimation for automated straddle carriers using smart sensors

Considering the harsh environment of the port, automated straddle carriers, characterized by their large size, tall frame, and high center of gravity, may experience instability during steering and transportation due to inaccurate state estimation. Thus, this paper explores state estimation techniques for automated straddle carriers utilizing smart sensors which are capable of data measurement and processing. First, using the steering principles and lateral characteristics of automated straddle carriers, a dynamic linear model is established based on Newton’s second law of motion. Then, in order to enhance the reliability and flexibility of state estimation, a distributed smart sensor network structure is introduced. In addition, considering the challenge of unknown-but-bounded noise and the precision demands of the considered automated straddle carrier, a modified distributed set-membership estimation algorithm is proposed and is derived sufficient conditions for the existence of the estimation set for the considered automated straddle carriers. Finally, the effectiveness and superiority of the proposed method are demonstrated by performance analyses.

Distinguishing Jordan and Einstein frames in gravity through entanglement

Distinguishing Jordan and Einstein frames in gravity through entanglement

Gravity framing and composite action effects on residual drifts of steel SMFs

In this study, the effects of gravity framing and composite action on the residual drift performance of steel special moment frames (SMFs) are investigated. Four steel structures including 4-, 8-, 12-, and 20-story SMFs are selected, and nonlinear models are created by considering the effects of gravity framing and composite action and neglecting these effects. Nonlinear dynamic analyses are performed on the structures subjected to the design basis earthquake (DBE) level ground motions. Under the DBE hazard level, accounting for the effects of gravity framing and composite action can reduce the maximum of median residual interstory drift ratios between 32% and 74%, when compared with that obtained by neglecting these effects. Incremental dynamic analyses are performed on the structures assuming the maximum residual interstory drift ratio (MRD) as the engineering demand parameter and four MRD limit states of 0.2%, 0.5%, 1.0%, and 2.0% to assess the residual drift performance of the structures in a probabilistic framework. The results show that considering the effects of gravity framing and composite action leads to significant decreases in the mean annual frequencies of exceeding different MRD limit states (i.e., λMRD values). These effects have the lowest impact on the λMRD values when the MRD is 0.2%. However, they have the highest impact on the λMRD values when the MRD is 1.0%.

Flexural resistance of 3D cut welded joints between SHS columns and through I‐beams

AbstractSteel structures can be designed according to different framing methods depending on the location of Moment‐Resisting‐Frames (MRFs). In Europe and the United States, one‐way MRFs are widely exploited due to their ability to clearly identify the seismic and gravity frames and limit the use of expensive joints only in MRFs. Furthermore, this is the most appropriate solution if double‐tee columns are adopted since they can provide high strength and stiffness only in the plane orthogonal to their strong axis. Instead, two‐way MRFs are commonly used in Japan; this solution creates 3D seismic structures and requires the selection of columns able to provide enough strength and stiffness along both their axes. This is the reason why tubular columns are usually used in Japan. Nevertheless, the main drawback of this practice is the need to manufacture complex beam‐to‐column connections.In this framework, the recent introduction of 3D Laser Cutting Technology (3D‐LCT) in Civil Engineering provides a way to reduce this complexity. It allows manufacturing quickly 3D cutting shapes with high precision, optimising the welding quantity and costs. Moreover, all the operations are programmed and fully realised by the machine, avoiding any intervention of operators, eliminating human errors, increasing the quality level and saving time. An example of this simplification is given by connections between Square‐Hollow‐Section columns and passing‐through double‐tee beams. Nevertheless, the novelty of this solution represents a limit to its application in practice because no design equations are currently included in common standards.To fill this knowledge gap, this paper investigates the flexural behaviour of SHS columns to passing‐through double‐tee beam connections according to the component method approach. In particular, the study has been carried out through numerical and analytical activities devoted to providing design formulations.

Investigation of flocculation behavior of tailings during settling-concentration: influence of true density, particle size, and mud layer height

The rapid concentration of tailings is a crucial initial step in the cemented paste backfill (CPB) process, as it ensures the stability of the backfilling slurry concentration and the continuity of the backfilling process. The structure of flocs plays a pivotal role in tailings concentration, directly contributing to such critical technical parameters as settling speed and bottom flow concentration. However, most of the current studies focus on flocculant addition rather than the tailings slurry itself. Also, there is a lack of uniform characterization of the flocculant structure in the flocculation and settling system. This study establishes a semi-quantitative assessment system for evaluating the fine structure of tailings flocs based on indicators such as the exposure state of coarse particles, floc size, and floc compactness (porosity). The findings reveal that, during the settling process, the higher true density of tailings (3.156 g/cm3) and intermediate particles (40 wt% of 38 μm–74 μm particles) attenuates the clamping effect of turbulence on settling, leading to a faster settling rate to 0.65 cm/s and 0.29 cm/s respectively. Moreover, in the thickening process, tailings located at the bottom of the mud layer expedite the precipitation of interstitial water within the floc structure through the combined influence of gravity and rake frame shear. Consequently, a denser floc structure forms, as evidenced by a higher concentration of bottom flow at a macroscopic level. This conclusion provides a theoretical basis for faster preparation of highly concentrated tailings slurry in CPB.

Collapse risk of steel framed buildings with deep columns under tri-directional excitation

Deep steel columns are widely used in steel buildings with perimeter moment frames (PMFs). Although their seismic behavior has been well examined at the member level, their influence on frame collapse response requires further exploration, especially their interaction with composite slabs, gravity frames, and ground motion components. To address this shortcoming, the collapse risk assessment of a set of steel buildings with PMFs and deep columns is performed via two modeling approaches: the conventional planar frame and the sophisticated space frame. The models are capable of capturing the instability, fracture, and collapse behavior in frame systems. The simulation results show that each additional ground motion component applied promotes the development of collapse mechanisms and significantly increases collapse probability, and that composite slabs combined with gravity frames greatly improve collapse capacity despite introducing additional local failures. Moreover, limiting slenderness ratios and controlling local buckling of deep columns is essential to prevent frames from vertical progressive collapse (VPC) and ensure sufficient collapse resistance. The available highly ductile limits (HDLs) are accordingly critiqued and revised. Due to the large discrepancies in the collapse risks determined by the two approaches, space frame modeling is suggested to accurately assess the collapse capacity of steel PMFs involving deep columns.

Plastic design of sustainable steel earthquake resistant structures

Earthquakes induce ultimate load conditions in most earthquake resistant structures and often lead to complete failure and disposal. Seismic sustainability is a limit state condition with a view to revival, reuse, and environmental protection. In the present context, sustainable seismic design implies planning for controlled energy dissipation, sequential failures, collapse prevention, construction economy and post-earthquake realignment and repairs. However, regardless of savings and environmental improvements unless an earthquake resistant structure is designed for the purpose, it would be disposable with greater monetary loss and harm to the environment. It has been found that steel mixed multiple seismic systems are well-suited for sustainable seismic design. Mixed multiple structures are combinations of two or more low/controlled damage ductile structures, an articulated gravity frame, a collapse preventive, hybrid, rigid rocking core, and a phantom P-delta system acting together to form a repairable archetype. Each earthquake resistant system is equipped with replaceable energy dissipating and fail-safe devices. Such arrangements call for applications of Plastic Design and Performance Control principles, rather than conventional methods of approach. This in turn calls for development of modern design rules, technologies and details that govern the behavior of such systems equipped with replaceable energy dissipating devices. In the interim several observations that reduce the task of otherwise cumbersome analysis to simple rules of response have been introduced.

Spinning (A)dS black holes with slow-rotation approximation in dynamical Chern-Simons modified gravity

One of the most crucial areas of gravity research, after the direct observation of gravitational waves, is the possible modification of General Relativity at ultraviolet and infrared scales. In particular, the possibility of parity violation should be considered in strong field regime. The Chern-Simons gravity takes into account parity violation in strong gravity regime. For all conformally flat spacetimes and spacetimes with a maximally symmetric two-dimensional subspace, Chern-Simons gravity is identical to General Relativity. Specifically, the Anti-de Sitter (A)dS-Kerr/Kerr black hole is not a solution for Chern-Simons gravity. The slow-rotating BH and the quadratic order in spin solutions are some of the known solutions to quadratic order in spin and they are rotating solutions in the frame of dynamical Chern-Simons gravity. In the present study, for the (A)dS slow-rotating situation (correct to the first order in spin), we derive the linear perturbation equations controlling the metric and the dynamical Chern-Simons field equation corrected to the linear order in spin and to the second order in the Chern-Simons coupling parameter. We show that the black hole of the (A)dS-Kerr solution is stronger (i.e. more compact and energetic) than the Kerr black hole solution and the reason for this feature comes form contributions at Planck scales. Moreover, we calculate the thermodynamical quantities related to this black hole. Finally, we calculate the geodesic equation and derive the effective potential of the black hole.

Trade relationship of Vietnam from the perspective of the China-US trade War 2019: A comparison study using the Gravity Model

Purpose: This study aims to evaluate the determinants of the trade relationship between the two largest trading partners of Vietnam, the United States, and China.
 Methodology: This study is completed using the gravity model for time series data from 1986 to 2019.
 Main Findings: The study found that the economic growth rate plays a crucial role in stimulating the trade flow. Both trade relationships fit with the practical approach of the gravity model, stating that trade flow increases between countries with different income levels. The most important finding of this study lies in the results regarding the impact of the trade war 2019 between the United States and China. The trade war 2019 can be compared with the study in previous 2015 on trade agreements between ASEAN and China produced trade diversion.
 Implications: As China expands its markets among ASEAN countries, Vietnam should diversify its export markets to improve its export flow in the trade agreement. But export and import correlation compared the effect of US – VN and China – VN change in the period of a trade war after five years.
 Novelty: This paper has studied the determinants of trade flows between VN-US and VN-CN to provide a detailed comparison. The input and output stream in gravity frame.

Gravity, axion Chern-Simons Einstein, and black holes

The low-energy limit of string theory involves an anomaly-removing correction of the action of Einstein-Hilbert, which defines a practical idea: Chern-Simons (CS) modified gravity. The CS correction composes of the product of a scalar field with the Pontryagin density, in which the scalar field is considered as a background field (non-dynamical formulation) or as an evolving field (dynamical formulation). Different solutions of Einstein’s general relativity (GR) continue in the amended theory; a keyable exception is the Kerr metric, which has affected a search for rotating black hole solutions. In this study, we derive a black solution characterizing a rotating black hole within the non-dynamical and dynamical frame of CS axion Einstein gravity (CSAEG). The case of non-dynamical has no new physics different from GR, which is consistent with what is presented in the literature. The main merit of this study is that in the dynamical framework of CSAEG, we show that the scalar field has a dynamical value up to the first-order approximation and under some constraints between the unknown functions that characterize this theory. Moreover, we show that the function U that characterizes CS can help to weaken the singularity for the invariant ^{*} ! R R.

Binary Interaction with Multiple Fluid Type Cosmology under Modified Gravity Frame

Binary Interaction with Multiple Fluid Type Cosmology under Modified Gravity Frame

Effect of interior gravity framing system and composite floor slab action on the lifetime seismic risk assessment of steel frame buildings subjected to mainshock–aftershock sequence

The structural analysis practices of steel moment-resisting frame buildings often neglect the participation of the interior gravity frames and composite floor slab action in their lateral strength and stiffness. In addition, the effects of aftershocks are frequently omitted in steel frame buildings’ seismic performance evaluations. This study investigates the effects of structural modeling assumptions and the incorporation of aftershocks on the seismic vulnerability and time-dependent lifetime seismic risk for a group of steel moment-resisting frame buildings. Three ductile steel moment-resisting frame buildings of four, eight, and twelve stories are examined in this study. The results indicate that the seismic performance of steel special moment-resisting frame buildings is substantially underestimated when based on structural models that ignore additional sources of lateral stiffness and strength owing to the interior gravity frame system and the composite floor slab action. In addition, when ignoring aftershocks from the seismic performance assessment, the possibility of catastrophic failure could be underestimated by a factor of 11 at the end of an assumed 50-year lifetime for the steel frame buildings, underscoring the need to account for aftershock effects in evaluating the collapse safety of the selected buildings.

Structural integrity of composite floors in fire: A comparison of two large-scale experiments with varying slab reinforcement

This paper presents a comparison of two compartment fire experiments performed on the 9.1 m × 6.1 m composite floors using a full-scale two-story steel gravity frame to study the influence of slab reinforcement on the overall structural integrity. The floor specimens were designed to achieve a 2-h fire rating but had dissimilar slab reinforcement. The Test #1 specimen had steel wire reinforcement of 60 mm2/m width as the minimum permitted in the United States practice whereas the Test #2 specimen was reinforced with deformed steel bars (230 mm2/m) determined by incorporating tensile membrane action. The Test #1 specimen exhibited mid-panel slab integrity failure before reaching the specified fire rating period. However, the Test #2 specimen exhibited much smaller concrete cracks until it was heated up to 131 min and retained the post-fire residual strength at least two times greater than the design demand at ambient temperature. This unique large-scale testing demonstrated that the appropriate slab reinforcement scheme can delay the vertical deflection of the heated composite floor and maintain the structural integrity at large vertical displacements over a longer duration of fire exposure.

System overstrength factor induced by interaction between structural reinforced concrete walls, floors and gravity frames: Analytical formulation

In multi-storey structural wall buildings, the structural walls are required to resist additional shear force due to their interactions with the floors and gravity-resisting system, which is not fully catered for in current seismic design provisions and assessment guidelines. This paper scrutinizes the mechanics of the interaction between structural reinforced concrete (RC) structural walls, floors and gravity frames in multi-storey RC structural wall buildings during elastic and nonlinear response phases. It also investigates the implications of this interaction on design of multi-story RC wall buildings. Generic expressions are derived to predict the drift and rotation profiles of multi-storey RC wall buildings. Then, a simple hand calculation method is developed to estimate the system (moment) overstrength of multi-storey RC wall buildings due to system (wall-floor-frames) interaction. The proposed method is applied to a prototype building with different slab dimensions and stiffness, and verified by comparing with the system overstrength factor obtained using finite element analysis. The simplified method estimates, and the nonlinear finite element analyses results agree, that a system overstrength factor of 1.7 can be used to account for the 3D interaction between the structural walls, floors and gravity frames in design and assessment of typical ductile RC wall buildings.

Influence of Gravity Framing on the Collapse Probability of Steel Buildings with Special Moment Frames

This paper presents the influence of gravity framing on the collapse risk of steel frame buildings with perimeter special moment frames (SMFs) designed in Turkey. For this, four- and eight-story buildings have been designed considering the related current specifications and codes. Header end-plate connections are used for the beam-to-column joints of the gravity frame system. A nonlinear analytical model that simulates the hysteretic behavior of header end-plate connections is calibrated with past experimental data. Nonlinear static pushover analysis (NSPA) and nonlinear response history analyses (NRHAs) were implemented for both four-story and eight-story SMFs with and without the gravity framing to quantify their collapse performance and monitor the system-level seismic response of the building through collapse. The advantage of presence of the gravity framing is investigated and differences in structural responses between the models are also examined. When the models were excited by different ground motions, median responses of the detailed models showed an increase in lateral force carrying capacity and a decrease in first-story drift demand, compared to the nonlinear static pushover analyses results. Furthermore, the results demonstrate that gravity frames in a structure profoundly decrease the possibility of collapse.

Comparison of Simple and Advanced Methods of Analysis in the AISC Specification for Fire-Resistant Structural Design

AISC Specification Appendix 4 provides criteria to aid structural engineers in structural design for fire conditions. It includes an advanced method of analysis and a simple method of analysis. The simple method provides straightforward equations to determine member capacities at elevated temperatures. However, determination of demands on the structure (forces and deformations) due to elevated temperatures is less clear. This paper aims to minimize these gaps in knowledge. A comparison of these methods will be articulated through the analysis of a 10-story office building. The building is a steel structure with perimeter moment frames and a composite floor system that was designed for hazards in Chicago, Illinois. In order to conduct the advanced analyses, a three-dimensional (3D) finite element method building model was developed using ABAQUS. This model can simulate inelastic deformations, instability failures, connection damage at elevated temperatures, and the effect of temperature on strength and stiffness of materials. The simple analyses were conducted using SAP2000, a commercially available structural analysis and design software. A comparison of results from each method of analysis shows that for gravity framing members, the advanced method produced the longest fire-resistance rating. The fire-resistance rating determined from the simple method was more conservative, resulting in a shorter resistance rating. The simple method was also found to be the most conservative approach for the moment-resisting frame members, making it a less desirable method for designing the lateral system for fire than the prescriptive approach. Use of the simple method may be most advantageous for gravity framing applications only and may be overly conservative for considerations of the lateral framing system.

Shaking table test of a three-story frame with resilient variable friction braces

A novel resilient variable friction brace (RVFB) has been proposed to avoid the complex prestressing process of a traditional resilient brace. This study presents a shaking table test of the 1/3 scaled RVFB frame (RVFBF) to evaluate its seismic performance. In particular, the concept and mechanical model of the RVFB were introduced, including the theory of variable friction and stiffness. Then, a three-story steel RVFBF with pinned connections was designed, including one braced frame and two gravity frames. This arrangement guaranteed that the lateral force resistance was only provided by the RVFBs, while other components of the RVFBF were kept in the elastic stage. After the frame was tested under several earthquake conditions with increasing ground motion levels, the accelerations, drifts, and shear forces of the RVFBF were evaluated. The results demonstrated that the RVFB exhibited a novel flag-shaped curve with greater loading stiffness. Good agreement was verified between the mechanical and experimental results. Although the peak floor drift of the RVFBF exceeded 2.6% under the strongest ground motion level, the damage-free frame returned to the initial position with nearly zero residual displacements, and the braces had negligible performance degradation after the entire test. Therefore, a RVFBF that has satisfied seismic requirements can effectively control the structural damage and quickly restore its function after several earthquakes.