Core Wall Structure Research Articles

Preparation and performance study of photo-initiated self-healing self-warning microencapsulated coated fabrics

Microcracks on the surface and inside inevitably occur during processing and use. The use of photo-initiated, self-healing, self-warning microcapsules to repair and monitor these microcracks is of practical importance to prolong the life of coated fabrics. In this work, the microcapsules (EP/FA/SiO2) with SiO2 as wall material, epoxy resin, fluorescent agent and cationic photoinitiator as core material were prepared using the interfacial in situ polymerization method. The self-healing self-warning PVC coated fabric was obtained by scraper coating method. The self-healing, self-warning and mechanical properties of the coated fabric were characterized. The results show that the microcapsules have an encapsulation efficiency of 79 % and a core-wall structure. The wall thickness is about 200 nm and the particle size is 1.7 μm. The microcapsules have excellent thermal stability below 320 °C. The microcapsules have good dispersion in the PVC coating surface and the repair agent has good wettability in the PVC coating surface. When the cuts expand, the previously embedded microcapsules break open and release the fluorescent active ingredient and the repair agent of the capsule core. Under UV light irradiation, the scratches may show a yellow fluorescence to indicate the location of the damage to the coating. The repair agent (epoxy resin) fills the cuts and then polymerizes with the cationic photoinitiator under UV light. As the exposure time increases, the cut gradually narrows and the strength of the coated fabric increases. After 36 h of UV exposure, the cut disappears and the strength of the coated fabric is 742 N, reaching the strength (768 N) of the fabric before scratching. This indicates that the coated fabric has a good photo-initiated self-healing effect.

Seismic performance of confined prestressed hollow core wall panels part II: Numerical simulation and analysis

In Part I of this research, confined prestressed hollow core wall structures were proposed and experimental tests of 19 specimens were conducted to study its mechanical behaviors. In this part, a detailed finite element model was developed in ANSYS to provide a tool for further investigating the seismic behaviors of confined prestressed hollow core wall structures. Contact elements were applied to simulate the interaction between material interfaces. Techniques in ANSYS including coupling of degrees of freedom (CP) of overlapped nodes and deactivation of concrete elements (EKILL) were adopted, along with restart analysis (REST) to simulate nonlinear mechanical behaviors of the structural system. The developed modeling method was verified by the experimental test results and was shown to accurately predict the global and local behaviors such as failure modes and load bearing capacities of precast hollow core walls. Parametric analysis on shear span ratio, axial load ratio, rigidity of floor systems as well as strength of vertical wall-wall joints was conducted, and relevant design recommendations were provided for prestressed hollow core wall structures. Results show that for a ductile prestressed hollow core wall structure, the axial load ratio is recommended to be smaller than 0.06 and the story number less than 5. Influence of rigidity of floor systems requires further study with dynamic tests, but low-strength vertical wall-wall joint is highly recommended for this system. Two analytical mechanisms that are shear-flexural mechanism and truss mechanism were proposed for calculation of load bearing capacities. These two mechanisms provide good predictions for an upper bound and a lower bound for load bearing capacities of prestressed hollow core walls, respectively. From Part I and II of this research, the mechanical behaviors of prestressed hollow core wall structures are verified experimentally, numerically, and theoretically, and it is concluded that they can be used as a potential choice for low-rise buildings in rural areas.

CaAl–NO2 LDH hybrid self-healing microcapsules with chloride triggering: Towards synergistic corrosion resistance

The synergistic corrosion resistance microcapsules (SCRMs) were synthesized by utilizing CaAl–NO2 LDH (NO2-LDH) as chloride trigger and high-performance corrosion inhibitor to hybridize self-healing microcapsules. The morphology, chemical structure and self-healing performance of the microcapsules were characterized. The chloride triggering and corrosion resistance property of the SCRMs were evaluated. The interaction of hybrid wall, NO2-LDH and chloride ion was calculated by first-principles. The findings revealed that the microcapsules show regular spherical with obvious core-wall structure. EDS and chemical structure measurements confirmed that NO2-LDH was successfully embedded within the microcapsule wall. The SCRMs showed excellent corrosion resistance property in simulated chloride-contaminated concrete pore solution (SCPS), and the highest inhibition efficiency was 97.85%. The microcapsule wall was hybridized by NO2-LDH species through chemical pathways. The first-principles calculation results confirmed that Ca and Al species are the main factors for chloride ion immobilization of hybrid wall. The ion exchange process of microcapsules destroys the molecular force of NO2-LDH@ethyl cellulose hybrid wall and improves the mechanical triggering efficiency of microcapsules in cement-based composites.

Seismic response control of core wall structures using tuned viscous mass damper (TVMD) outriggers

This paper presents research on the seismic response control of core wall structures through the installation of innovative damped outriggers known as tuned viscous mass damper (TVMD) outriggers. In this novel system, the TVMDs are arranged vertically between the outrigger trusses/beams and perimeter columns. A simplified model based on the distributed-parameter system was developed to represent a core wall structure equipped with TVMD outriggers. The dynamic properties and seismic responses of high-rise buildings were calculated through a dynamic analysis of the simplified model in MATLAB. The results indicate that TVMD outriggers designed by using fixed-point theory not only suppress the dynamic responses for the target tuning mode, but also supplement additional damping to lower-order modes. When tuned to the second mode, TVMD outriggers with a mass ratio of 0.1 reduce the maximum inter-story drift and floor acceleration responses by 23.48% and 35.80%, respectively. In addition, the control advantages of TVMD outriggers were demonstrated through energy dissipation analysis and damper force decomposition. The vibration control performance of multiple TVMD outriggers was also investigated and was found to achieve superior seismic control with a significantly reduced demand on the TVMD parameters.

Study of Effective Length Factor of Frame–Core Wall Structure with Cross-Layer Columns

The aim of this study was to examine the effective length factor of frame–core wall structures with cross-layer columns, which are relevant for current high-rise building construction. Using the finite element method, improved inflection point method (D-value method), and GB50017-2017, the study investigated how the height and distribution of cross-layer columns affect the lateral stiffness ratio, natural vibration period, member internal force, maximum interlayer displacement angle, and effective length factor of the column in the frame–core wall structures. However, the force acting in the frame in the weak axis direction that is considered in GB50017-2017 does not reflect the actual mechanical behavior. Therefore, when determining the effective length factor of cross-layer columns, the interaction between the remaining frames’ sub-structure and cross-layer columns is considered and the effective length factor is modified accordingly. A simplified model of a 140 m frame–core wall structure was established for analysis, and it was assumed that rigid links connect the frame and core wall hinged at both ends. The results show that increasing the height and number of cross-layer columns decreased the lateral stiffness ratio of the structure, and increased the maximum interlayer displacement angle and natural vibration period. Furthermore, the effective length factor of the structure decreased with an increase in height and the number of cross-layer columns. The modified effective length factor agrees well with the results obtained by the finite element method. These findings provide a useful reference for calculating the load-carrying capacity of cross-layer columns in engineering.

Effect of Interlayer Bonding Temperature on the Bending Properties of Asphalt Concrete Core Wall.

In the construction process of an asphalt concrete impermeable core wall, the interlayer bonding of the core wall is the weak link of the core wall structure and also the focus of construction, so it is important to carry out research on the influence of interlayer bonding temperature on the bending performance of an asphalt concrete core wall. In this paper, we study whether asphalt concrete core walls could be treated with cold-bonding by fabricating small beam bending specimens with different interlayer bond temperatures and conducting bending tests on them at 2 °C. The effect of temperature variation on the bending performance of the bond surface under the asphalt concrete core wall is studied through experimental data analysis. The test results show that the maximum value of porosity of bituminous concrete specimens is 2.10% at lower bond surface temperature of -25 °C, which does not meet the specification requirement of less than 2%. The bending stress, strain, and deflection of bituminous concrete core wall increase with the increase of bond surface temperature, especially when the bond surface temperature is less than -10 °C. If the lower bonding surface temperature is less than 10 °C, the upper layer of asphalt mixture with large grain size aggregate cannot be effectively buried in the low bond surface, resulting in flat fracture and brittle damage to the specimen, which is detrimental to construction quality; therefore, the bonding surface should be heated so that the temperature of the bottom bonding surface is 30 °C. If the lower bonding surface temperature is 10 °C or above, no heating is required.

Beam-Truss Models to Simulate the Axial-Flexural-Torsional Performance of RC U-Shaped Wall Buildings

Reinforced concrete (RC) core walls are commonly used to provide buildings with lateral and torsional resistance against the actions of wind and earthquakes. In low-to-moderate seismic regions, it is not unusual to find a single peripheral core wall that alone should resist these actions, where the torsional (rotational) twist cannot be neglected. It has previously been difficult to have confidence in simulating the axial-flexure-torsion behavior of these RC core walls, primarily due to: (i) some types of modelling approaches being unable to appropriately account for the shear-flexural action, as well as torsional response; and (ii) the scarcity of experimental data, particularly for walls under torsional loads, which would be required to validate such models. In this research, beam-truss models (BTMs), which correspond to an interesting compromise between detailed modelling and practical applications, were used to simulate the in-plane and diagonal flexural response of RC U-shaped walls. Furthermore, the global torque-rotation results from a recent experimental wall test provided the evidence to further validate this powerful modelling technique. A case study building, comprising an RC U-shaped core wall structure with varying eccentricity values, was evaluated for an earthquake event with a 2475-year return period in the city of Melbourne, Australia, using the capacity spectrum method. Nonlinear static pushover analyses showed that, depending on the magnitude of torsion, the in-plane flexural strength and displacement capacity can be significantly reduced. The results from this research emphasize the importance of including torsional actions in the design and assessment of reinforced concrete buildings.

Optimal Design of Mega-Frame Core Wall Structures Equipped with Viscous Damped Outriggers for Human Comfort Performance under Wind Loading

Megatall and supertall buildings often adopt megastructure systems characterized by secondary structure systems, and the serviceability problem caused by wind-induced vibrations often becomes the dominant factor in the structural design. Because the deformation of a supertall building usually presents bending characteristics, a viscous damped outrigger can reduce the wind-induced vibration of a supertall building with the installation of a small number of viscous dampers. However, time history analysis of the prototype model considering the nonlinear characteristics of viscous dampers is time-consuming, which is not conducive for iterative design optimization. Additionally, the conventional simplified model composed of one cantilever beam cannot be used for the analysis and design of a viscous damped outrigger. In this study, a simplified wind-induced vibration prediction model is proposed based on the mechanical characteristics of megastructures. This simplified model is a plane model that includes both core walls and frames whose member size can be extracted from the original structure. Parametric analysis shows that the simplified model has high acceleration prediction accuracy. An optimal design method combined with the simplified model, which aims to minimize the damped outrigger system cost, is proposed. A 600-m supertall building is presented as a case study. The accuracy and effectiveness of the simplified model and the optimal design method proposed in this study are illustrated. Thus, applying this optimal design method in combination with the simplified model can save significant analysis and design time and is conducive to the application of viscous damped outriggers in practical engineering.

Seismic performance assessment and rating for a flat-slab RC core wall structure in Bucharest, Romania

This study focuses on the assessment of the seismic performance for a 12-story high reinforced concrete structure situated in Bucharest, Romania. The structural system is common for many newly built office buildings in Bucharest and it consists of a flat slab with columns and thick reinforced concrete core walls. The seismic performance of the structural system is evaluated using ground motions with considerable long-period spectral amplifications, that are characteristic to Bucharest area during large magnitude Vrancea intermediate-depth earthquakes. The building is the first office building having a flat slab structure with core walls designed for the seismic conditions of Bucharest which is evaluated according to US Resiliency Council criteria and according to recent criteria proposed by Italian Guidelines. The results of the seismic rating show that it can be classified as a 3-stars for the safety criterion and as a 4-stars one for both the recovery time and repair cost criteria according to US Resiliency Council criteria. Moreover, the building can be graded as a class A one based on the criteria from the Italian Guidelines.

Experimental study on orthogonal joints in cross-laminated timber with self-tapping screws installed with mixed angles

Cross-laminated timber (CLT) is increasingly being used in lateral load resisting systems of multi-storey buildings. Conventional in-plane CLT shear walls can be transformed into CLT core-wall structures with enhanced lateral strength and stiffness when the individual walls are connected orthogonally. In this paper, experimental studies are presented on orthogonal CLT joints with self-tapping screws (STS) installed with mixed angles, i.e. different installation angles between the STS axis and the plane of the CLT surface. A total of 59 orthogonal joint specimens were tested in 9 different configurations to derive the relevant joint performance parameters from monotonic and cyclic tests. The joint specimens used five-layer and seven-layer CLT panels connected by ∅8 mm or ∅12 mm STS. Different ratios of STS installed inclined and STS installed at 90° to the CLT surface were investigated to determine an optimum ratio of STS for enhanced joint performance. It was found that a ratio of one 90° STS for every two inclined STS ensured significant increase in ductility and displacement capacity of approximately three times when compared to specimens with only inclined STS. A minimum moderate ductility was achieved in all test series where the primary failure mode was STS withdrawal. It was found that 90° STS contributed to both strength and stiffness in joints that also contained inclined STS. The average experimental overstrength was 1.7 for most joint configurations. Existing analytical models were adequate in estimating strength but inadequate to estimate stiffness.

Cyclic behavior of c-shaped composite plate shear walls – Concrete filled

A Composite Plate Shear Wall/Concrete Filled (C-PSW/CF) is a special lateral-force resisting system consisting a sandwiched panel of two steel plates with concrete infill in between them, ideally suited for core-wall structures in high-rise construction. The steel plates are connected to each other using tie bars that are embedded in the concrete infill and, in some instances, steel-headed stud anchors. This research project was conducted to investigate the cyclic lateral load behavior of these walls, in terms of strength, and drift capacity. The testing program includes two large-scale C-shaped concrete filled composite plate shear core walls subjected to flexure and axial loads together. Their dimensions were the same, but different axial loads were applied up to 19% of axial loading capacity. The composite behavior and the plastic hinge development were investigated and compared to results from plastic moment calculations. This provides valuable results on the expected behavior of one composite cross-section that is frequently used in full core wall. This is done to support the development of design guidelines for high-rise core-wall steel buildings having C-PSW/CF as the primary lateral force resisting system.

Evaluation of Simplified Analysis Procedures for a High‐Rise Reinforced Concrete Core Wall Structure

Nonlinear response history analysis (NLRHA) procedure is one of the most precise and accurate numerical method to compute the seismic demands of high‐rise structures but is complex, rigorous, and time‐consuming and requires a lot of expertise for nonlinear modelling and results interpretation. Therefore, practicing engineers in developing countries like Pakistan still use the simplified analysis procedures to compute the seismic demands. Among the simplified analysis procedures, equivalent lateral force and response spectrum analysis procedures are widely used for the design purpose. However, other procedures have also been proposed in the recent past to accurately capture the higher mode effects in mid‐to‐high‐rise structures. In the current study, results of a forty‐story core wall building are used to check the relative accuracy and ease of application of different simplified analysis procedures. Furthermore, a modal decomposition technique is used to separate the modal responses from the NLRHA results, and a mode wise comparison of different demand parameters for different simplified procedures is performed. The current study has been used to clearly identify the reasons of inaccuracies in different simplified procedures. Furthermore, a simplified analysis procedure is proposed to accurately estimate the seismic demands of high‐rise buildings and the possible solutions to improve their predictions.

BEHAVIOR AND DESIGN OF FIN WALLS AT THE PERIPHERY OF STRONG CORE WALL STRUCTURE IN HIGH-RISE BUILDINGS

In high-rise buildings, lateral loads, such as wind and seismic loads, are frequently resisted by reinforced concrete (RC) structural walls. Behavior and design of fin walls at the periphery of strong core wall structure in high-rise buildings were not analyzed seriously despite their structural importance. Using elastic design/analysis methodologies for the design of high-rise RC fin walls, it is shown that elicited reinforcement ratios are too high, the economic feasibility and constructability thus becomes worse and the ductile failure mode can not be assured. In the present study, the current design process of these fin walls is investigated by analyzing their structural behavior. According to the investigation of the current design and elicited results, high-rise RC fin walls are coupled by beams although they are located on another line and apart from each other, which is main cause of high reinforcement in high-rise RC fin walls. In the present study, a literature review has been conducted to recommend the alternative design method for high-rise RC fin walls under lateral loads, and inelastic analysis has been performed to verify the design method.

Forward directivity near-fault and far-fault ground motion effects on the responses of tall reinforced concrete walls with buckling-restrained brace outriggers

In this paper, responses of reinforced concrete core-wall structures connected to the outside columns by buckling-restrained brace (BRB) outriggers in tall buildings were investigated. These buildings are subjected to forward directivity near fault (NF) and ordinary far-fault (FF) ground motions. According to the current codes for the DBE level, the response spectrum analysis procedure was applied to analyze and design the structures. The nonlinear fiber element approach was used to simulate the reinforced concrete core-walls. Nonlinear time history analysis was implemented using 14 NF as well as 14 FF records at MCE level. In the core-wall, the results show that the mean moment demand envelope as well as the mean shear demand envelope obtained from the NF records are approximately similar to the corresponding demand envelope from FF records. The reason has to do with extending plasticity all over the RC core-wall which is subjected to both sets of records. The overall responses of the reinforced concrete core-wall with BRB outrigger system is in acceptable range both for NF and FF earthquakes. In this study, the largest curvature ductility demand in the reinforced concrete core-wall took place at levels just above the outriggers.

Earthquake effects on the energy demand of tall reinforced concrete walls with buckling-restrained brace outriggers

Reinforced concrete core-wall structures with buckling-restrained brace outriggers are interesting systems which have the ability to absorb and dissipate energy during strong earthquakes. Outriggers can change the energy demand in a tall building. In this paper, the energy demand was studied by using the nonlinear time history analysis for the mentioned systems. First, the structures were designed according to the prescriptive codes. In the dynamic analysis, three approaches for the corewall were investigated: single plastic hinge (SPH), three plastic hinge (TPH) and extended plastic hinge (EPH). For SPH approach, only one plastic hinge is allowed at the core-wall base. For TPH approach, three plastic hinges are allowed, one at the base and two others at the upper levels. For EPH approach, the plasticity can extend anywhere in the wall. The kinetic, elastic strain, inelastic and damping energy demand subjected to forward directivity near-fault and ordinary far-fault earthquakes were studied. In SPH approach for all near-fault and far-fault events, on average, more than 65 percent of inelastic energy is absorbed by buckling-restrained braces in outrigger. While in TPH and EPH approaches, outrigger contribution to inelastic energy demand is reduced. The contribution of outrigger to inelastic energy absorption for the TPH and EPH approaches does not differ significantly. The values are approximately 25 and 30 percent, respectively.

Seismic assessment of RC core-wall building capable of three plastic hinges with outrigger

Summary In a core-wall structure with buckling restrained braces (BRB) outrigger, locations of the plastic hinges are influenced by the outrigger action. Therefore, the designer should consider the issue and use suitable details in the plastic hinge area. The essential questions that arise here are the plastic hinge location and the design moment demand used for design of this kind of structure. In this paper, responses of the core-wall buildings with BRB outrigger designed by using the traditional response spectrum analysis procedure are assessed by implementing the nonlinear time history analysis. The result demonstrates that the plasticity can extend over anywhere within the core-walls specially, at the base and above or below the outrigger levels. Formation of three plastic hinges in the core-wall is recognized suitable for the system. To control the plasticity extension in the core-wall, it is recommended that a new modal combination method be applied to calculate the moment strength of the three plastic hinges over the height. A capacity design concept is used to design other regions of the core-wall where the plasticity does not extend to. The proposed procedure improves behavior of the system by restricting the plasticity extension to the predefined plastic hinge regions. Copyright © 2016 John Wiley & Sons, Ltd.

Energy dissipation of tall core-wall structures with multi-plastic hinges subjected to forward directivity near-fault and far-fault earthquakes

SUMMARY In this study, different energy components in the tall reinforced concrete core-wall buildings with numerous plastic hinges over the height are investigated using nonlinear time history analysis. The effect of near-fault and far-fault earthquakes is compared. The idea of one-plastic, two-plastic, three-plastic and whole-plastic hinge approaches along the core wall is examined. The input energy, inelastic, damping, kinetic and elastic strain energy during the earthquakes are studied. The results show that a large energy quantity transfers to the structure at the arrival time of the near-fault motion pulse. Inelastic energy distribution over the height shows a considerable amount of inelastic energy dissipation occurring at the base and above the mid-height of the walls. Copyright © 2016 John Wiley & Sons, Ltd.

Testing and Behavior of Coupled Shear Wall Structure with Partially Post-Tensioned Coupling Beams

A 40%-scale coupled core wall structure with C-shaped wall piers and novel unbonded post-tensioned (PT) coupling beams was tested under quasi-static reversed-cyclic lateral loads combined with tributary gravity loads. This paper describes the design, analysis, and testing of this specimen, which included the bottom three stories, the tributary floor slabs, and a large portion of the foundation from an eight-story prototype structure. The upper five stories of the prototype structure were simulated analytically to impose forces and moments at the top of the test specimen. In addition to conventional sensors, the specimen was monitored using 14 digital image correlation (DIC) sensors, providing near-full-field response data of the most critical regions. Overall, the structure performed as predicted, validating the design approach. Strength loss at the end of the test was largely caused by the fracture of the vertical reinforcing bars in the wall pier toes at the base. The coupling beams performed well, demonstrating the advantages of the new PT system.

Analysis about the Influence of Clay Core Wall Structure towards the Slope Stability of High Embankment Dam

As the main part of the anti-seepage system, core wall is a key point in the design of high em-bankment dam. The dam slope stability is a major factor for the type of core wall. But it is still unclear what effects the core wall structure might have on the slope stability. Based on practical projects of high embankment dam in Nuozhadu, Lianghekou and Shuangjiangkou, this paper analyzes safety factors and dangerous slip sur-faces of dam slopes of high embankment dams in both straight and slanting core wall structures and compares the influences of different core wall structures on the slope stability of high embankment dam through numerical calculations. The safety margin of the embankment dam of straight core wall is larger than that of slanting core wall in the operating condition of the reservoir water level’s drawdown. Compared with that of the straight core wall scheme, the position of the dangerous slip surface of the downstream dam slope is closer to the dam crest in the slanting core wall scheme.

Computer Simulation and Energy-Saving Analysis of a Composite Steel Residential Building

The steel frame-reinforced concrete core wall structure is a typical composite structure, which has been applied to residential buildings for its excellent seismic behavior. In order to evaluate the energy consumption of existing residential buildings with composite structures, an on-site test on envelope of a typical composite steel residential building in cold region is performed; the heat transfer coefficient K of envelope and its actual energy consumption are calculated and analyzed by use of the testing data. Based on that, a simplified computer model is established and verified. Parameter analyses are carried out on two main influential factors. The results indicate that the building envelope has good heat storage property and it could keep indoor thermal stability; the steel frames and windows have heat bridge effects ； the tested building only meet requirements of energy-saving 50%-standard, instead of 65%-standard; the traditional calculation method for energy consumption overestimates the energy consumption of buildings; the most effective way to reduce heating consumption is to improve thermal performances of external walls; the thickness of insulation layers should be confined in an appropriate range. Finally the thermal design recommendations for composite steel residential buildings are proposed.