Monolithic RC Research Articles

Cyclic loading experiments on seismic performance of precast concrete superposed shear walls with CFST end columns

The seismic performance of precast concrete shear walls is a major concern when considering their application in earthquake-prone regions. To improve the seismic performance and constructability of conventional precast concrete superposed shear walls, an innovative design, termed Precast Concrete Superposed Shear Walls with CFST End Columns (PCSSWEC), has been proposed. Given the limited research on the seismic performance of PCSSWECs, cyclic loading experiments were conducted on three full-scale PCSSWEC specimens and one monolithic RC shear wall specimen. The design axial compression ratio (ACR) and the thickness of the steel tube were employed as research variables. Experimental observations and results gave a comprehensive view of the hysteretic behavior of PCSSWECs, reflecting a favorable seismic performance (in terms of failure modes, global and local damage, force-displacement responses, load-bearing capacity, stiffness and strength degradation, deformability, ductility, and energy dissipation capacity). The experiment also revealed significant differences between PCSSWECs and monolithic RC shear walls in concrete crack development and deformation characteristics, confirming that the CFST columns and the wall panel could work together until the failure phase. Moderately increasing the ACR (0.3–0.5) was beneficial for PCSSWECs. However, increasing the steel tube thickness (3.5 mm–5.0 mm) could lead to unfavorable degradation in strength and stiffness and weaken ductility. In addition, a simplified method was proposed to evaluate the flexural strength of PCSSWECs.

Experimental recognition of seismic performance of simple bolt-connected precast frame by comparing with equal stiffness cast-in-situ frame

Multi-story industry buildings composed of precast concrete members and simple bolt-type connections are widely constructed in the world, and there is enormous need for future construction market. Based on the equal stiffness and stiffness distribution along the height, a 1/5-scale precast RC frame utilizing simple bolt-type connections and a reference cast-in-situ monolithic RC frame were designed and constructed to conduct shaking table tests. According to the test results, the seismic responses, failure modes and energy dissipation behaviors of the two models were analyzed and compared. The vibration modes of the precast frame performed bending deformation pattern, while the cast-in-situ one presented shear deformation pattern. The damage and inter-story drift of the precast frame was comparatively uniformly distributed along the stories, whereas that of the cast-in-situ frame was concentrated in the first story. The energy dissipation capacity of the precast frame was inferior to that of the reference frame, as the bolt-type connections couldn't have plastic damages and plastic hinges that occurred in the cast-in-situ joint zones. In general, the global seismic performance of the precast frame was close to the reference frame and its collapse resisting capacity under severe earthquakes was reliable. Some serious local failure modes and less of energy dissipation capacity of the precast frame should be concerned in high seismic regions.

Experimental Study on Bending Performance of High-Performance Fiber-Reinforced Cement Composite Prefabricated Monolithic Composite Beams

To enhance the mechanical properties and damage resistance of prefabricated monolithic composite beams, this study introduces HPFRCC precast mold shells as a replacement for ordinary concrete in the construction of prefabricated monolithic composite beams. These HPFRCC precast mold shell prefabricated monolithic composite beam members are then subjected to experimental investigations to analyze their flexural properties. The results of the study indicate that the U–shaped HPFRCC precast mold shell exhibits excellent bonding with the post-cast concrete, with no significant peeling observed. Moreover, compared to ordinary cast-in-place monolithic RC beams, the HPFRCC/RC prefabricated monolithic composite beams demonstrate a 17.2% increase in peak load and a 24.55% increase in yield load. Similarly, the HPFRCC/RC prefabricated monolithic composite beams show an 8.1% increase in peak load and a 5.59% increase in yield load compared to ordinary RC composite beams. In comparison to both ordinary cast-in-place monolithic RC beams and ordinary RC composite beams, the cracks observed in the HPFRCC/RC prefabricated monolithic composite beams are denser and finer, with a smaller crack development rate and width. These findings suggest that the incorporation of HPFRCC materials improves the damage resistance of the beam members.

Seismic Response of Monolithic and Precast RC Building for Site-Specific Conditions

This paper investigates the seismic response of a rigid and flexible RC building by performing nonlinear time history analysis (NLTHA). In the present study, the numerical model of a 5-storey monolithic RC (MRC) and 5-storey precast RC (PRC) buildings are developed in SAP2000. The buildings are assumed to be situated in Assam and a real Silchar site from Assam is considered. For the NLTHA, six spectrum compatible time histories (SCTH) are considered. The first set comprises of 3 SCTH matched to the Indian seismic code design spectra (ISCDS) and the second set comprises of 3 SCTH matched to the site-specific elastic response spectra (SSERS). The NLTHA results show that the roof displacement of the MRC building is less as compared to the PRC building for all the considered cases. However, the response for both the structures for SSERS compatible time histories is more significant as compared to the ISCDS compatible time histories. It is interesting to note that when the energy dissipation in the structure is evaluated for ISCDS compatible time histories, the damage in PRC building is negligible as compared to MRC building. Moreover, for SSERS compatible time histories, the damage in both the buildings are comparable. The results show the importance of site-specific study and its response on the structure behavior.

Experimental validation on seismic performance of a monolithic precast RC shear wall structure with novel connections

A novel monolithic precast concrete shear wall structure system was proposed, with four connector types: “cast-in-site elbow reinforced concrete joints,” “dry connectors,” “shaped steel shear keys,” and “shaped steel boundary elements” based on welding process with stable and high quality. The first two connect walls horizontally and the other two connect walls between adjacent stories. A high precast ratio, over 60%, can be achieved. To evaluate the strength, stiffness, ductility, and energy dissipation capacity of the proposed system, a full-scale three-story model was tested quasi-statically in the two horizontal directions. The model showed strong spatial response, demonstrating sufficient strength and stiffness to resist severe earthquakes. The coupling beams suffered shear failure damage. The connectors sustained large internal forces, surviving under simulated severe earthquake conditions. The external thermal insulation layers remained firmly attached to the precast wall panels, satisfying the design objectives.

Strengthening and SHM system installation on RC slab using non-linear FE analysis

Re-life of aged load-bearing structures may be more efficient and economical than complete re-building. Nowadays, the strengthening of an RC structure can be designed using non-linear FE analysis, taking a realistic structural behaviour into account. Within the current article, this process is demonstrated in connection with the strengthening of a monolithic RC slab. The slab must be strengthened due to a change of function which increases live load. To ensure satisfactory operation in SLS for increased load, the flexural strengthening of the slab by CFRP strips and bonded steel plates was considered. Static verification of the slab for original and increased loads is performed by linear FE analysis. The load-bearing capacities of the original and the strengthened slabs are also determined by non-linear FE calculation. A comparative analysis of the results highlights the effectiveness of different strengthening methods in increasing the stiffness and SLS capacity of the slab. To perform real-time monitoring of the slab in question, an SHM system is also suggested with the installation of three different types of sensors. This system increases the safety of operation and reduces future maintenance and strengthening costs.

INDUSTRIAL TOWER LIFE CYCLE EXTENSION ACCORDING TO SIKA TECHNOLOGIES

Some aspects of the life cycle extension of RC tower which is a chemical enterprise was described. This technological tower of ammonium seliters granulation has a height of +71,30 m. From this height to the Mark +46,10 mthe tower is made in a metal frame with diameter at the axes of the column22,56 m. The facade of this part is made of mounted keramzytoconcrete panels and in line constructional glazing. Between the marks 0,00 ÷ +46,10 mthe building has a monolithic RC trunk, which has a cylindrical outline in the form of a shell with an outer diameter of12,88 mand a thickness of0,3 mwalls. During 46 years of operation in chemical influences, the surface layers of the tower’s concrete trunk significantly lost its design strength. According to the results of almost regular surveys, the category of RC trunk technical condition was consistently classified as unsuitable for normal maintenance. A significant deterioration of the technical condition came in 2017, after which the building was withdrawn from the technological process, which gave impulse to the searching process of technical solution for the strengthening and chemical protection of the tower to prolong the life cycle of the entire facility. As a result of the survey the construction of the tower shall strengthening by a system of radial and vertical stiffening ribs was developed. It required a substantial unloading of the entire tower. Swiss concern Sika, one of the world leaders in the field of development and implementation of innovative technologies and materials for construction and industry, successfully implements its developments in Ukraine. For the above-described construction the firm Sika offered repair and chemical protection systems against aggressive influences for the internal and external surfaces of the tower shell, which will allow to significantly protect it and prolong the life cycle of structure.

Dynamic response of precast concrete beam with wet connection subjected to impact loads

Precast concrete (PC) structures are increasingly employed in recent years due to their advantages in better construction quality control and saving construction time. Most of the existing researches have been carried out to study the seismic performance of PC structures. The investigation of PC beams with wet connection under impact loads is, however, very limited in open literature. In this paper, numerical studies are conducted to investigate the dynamic behavior of PC beams with wet connections subjected to impact loads by LS-DYNA. The numerical models are calibrated with the experimental results from other researchers. With the calibrated numerical model, the dynamic performance of PC beams is compared with that of monolithic RC beams. It is found that the impact forces on PC and RC beams are similar due to the identical contact stiffness at the impact location. However, the interfaces between PC components and cast-in-place concrete (CIPC) components as well as grout sleeves used to connect longitudinal rebars cause uneven stiffness distributions of PC beams, hence resulting in different failure modes of PC and RC beams. Parametric studies are conducted to investigate the effects of three parameters, i.e., impact energy with respect to impact mass and velocity, inclination angle of the drop weight, and concrete strength on the dynamic response of PC beams subjected to impact loads. The results obtained in this research shine some lights on the impact performances of PC beams.

Precast prestressed concrete frames for seismically retrofitting existing RC frames

A precast prestressed concrete frame system with mild press joints is introduced for the seismic retrofit of existing reinforced concrete frames. Cyclic loading tests are conducted on precast prestressed concrete and cast-in-situ reinforced concrete frame subassemblies to investigate the hysteretic behavior and damage characteristics of the frames. The test results demonstrate the damage-tolerance of precast frames in terms of well-controlled cracking and minimized residual drift compared to monolithic RC frames. A simplified numerical model is introduced to simulate the hysteretic behavior of mild press joints. The dynamic seismic response of a prototype building retrofitted by the proposed method is evaluated by numerical analysis. Two retrofit plans with different attached precast frames are compared. The results suggest that a partial retrofit of certain lower stories, which has been a common practice in Japan, may create drift concentration in the upper stories of a building.

Finite element analysis of cast-in-situ RC frame corner joints under quasi-static and cyclic loading

DOI: 10.7764/RDLC.18.3.579 Many types of computer software are currently available for the numerical modeling of monolithic RC structures; however, the accuracy of the numerical models created with the programs can only be acceptable by using a well-developed modeling method. We present the behavior of monolithic RC frame corners and beam to column joints for quasi-static and cyclic lateral loads, using numerical models created by our modeling method. Several laboratory experiments have already been carried out to investigate the failure of the joints and the behavior of these unique connections. In this paper, we made three-dimensional nonlinear FE body models with different reinforcement shapes, based on actual laboratory tests. We present the behavior of the joints in case of monotonic increasing quasi-static and cyclic changing loads. The results of laboratory experiments found in the literature and finite element calculations are compared and the conclusions that can be drawn from them are summarized within this article.

Reversed Cyclic Loading Test on Emulative Hybrid Precast Concrete Shear Walls under Different Vertical Loads

An experiment was carried out to investigate the seismic performance of hybrid precast concrete shear walls, which aimed to emulate the monolithic RC wall by incorporating unbonded post-tensioned high-strength strands and vertically connected reinforcing bars by grouting across the horizontal joint for lateral resistance. The unbonded tendons provided the pre-compression and the recentering force. The grouted reinforcing bars were used to provide the bending strength, reduce the gap opening size, and eliminate the horizontal slippage along the joint. Three full-scale emulative hybrid wall specimens under different vertical loads and one monolithic RC wall specimen for reference were subjected to reversed cyclic loading. The test results showed that, the emulative hybrid specimens, with vertical load less than or equal to that of the monolithic specimen, exhibited good lateral performance and the seismic properties, including strength, stiffness, ductility and energy dissipation, were comparable to that of the monolithic specimen. As the vertical load increased, the strength and stiffness were enhanced, however, the energy absorbing capacity was obviously decreased.

Seismic researches on a new assembled monolithic RC structure based on IDA

A new assembled monolithic RC structure can be formed by using a new light assembled shear walls and frame joints. Seismic researches on the new RC structure can be realized by method of IDA. A calculation model of the new RC structure based on a real engineering is established through finite element method. Twenty far field seismic waves were used as seismic input according to request of ATC-63. Dynamic responses of the RC structure under different earthquake excitations were obtained by incremental dynamic analysis based on Opensees software. The seismic behavior of the new assembled monolithic RC structure was also studied according to the current Chinese seismic design code. The results show that this kind of structure can meet the requirements of related specifications in terms of seismic behaviors, which can provide some references to engineering design and research.

Switching SiC Devices Faster and More Efficient Using a DBC Mounted Terminal Decoupling Si-RC Element

Large power modules include several parallel mounted chips per switch to raise active area and current. By the electro-mechanical connection interface, the resulting large parasitic inductance is a huge problem especially for very fast switching SiC devices. This challenge is handled by many approaches, but these recent developments require additional development effort along all aspects of the power module, e.g. smart DBC layout, low inductive top side metallization, special terminal designs or additional pins. In this paper we demonstrate an approach to enable excellent switching performance with con-ventional power module technologies: By using a recently developed monolithic silicon RC (Si-RC) element to decouple the bus bar, this problem can be solved in a very efficient way. The Si-RC element is assembled directly adjacent to the power switches on the DBC. This allows a significant reduction of the SiC chip area by minimizing the power losses caused by the switching transients from the parasitic DC-link and module inductances.

Experimental study on emulative hybrid precast concrete shear walls

The reversed cyclic lateral loading experiments were conducted on three, full scale, emulative hybrid precast concrete shear wall specimens with different post-tensioned forces and one reference monolithic RC shear wall specimen, and the measured results were then discussed in this paper. The emulative hybrid wall combined grouted vertical reinforcements with unbonded post-tensioned high-strength multi-strand tendons for lateral resistance, attempting to emulate the cast-in-place RC wall. Because of the presence of the unbonded post-tensioned tendon, by contrast to the monolithic wall specimen, the emulative hybrid wall specimens possessed higher strength, higher stiffness, and smaller residual displacement. The opening gap, resulted from the discontinuity of concrete and the locally debonding of vertical connecting reinforcements, was limited mainly due to the vertical connecting reinforcements across the joint distributed over total cross-section. Meanwhile, the emulative hybrid wall specimens were capable of providing energy dissipation and ductility capacity comparable to that of the monolithic specimen, and the negative effect of the post-tensioned force on energy dissipation was more obvious than on ductility. Moreover, the post-tensioned tendon remained elastic throughout the test and the yielding of the connecting reinforcements was delayed.

Hard projectile perforation on the monolithic and segmented RC panels with a rear steel liner

Twenty-five shots of reduce-scaled projectiles perforation test on five configurations of monolithic and segmented RC panels with a rear steel liner were conducted. The impact resistances of layered bare RC and RC/steel composite targets were analyzed quantitatively based on the obtained striking and residual velocities of the projectiles, and the accuracy of the newly developed small-caliber accelerometer in recording the high-amplitude accelerations of the projectile is validated. The main conclusions are: (1) With the same overall thickness and projectile striking velocity, the stacked segmented targets have higher impact resistance than the spaced segmented targets. (2) For the spaced segmented targets with the same total thickness (i) the impact resistance of the monolithic RC plate is better than that of the segmented target, which is not dependent on the impact velocity as well as the rear steel liner is attached or not; (ii) the more the layers of the segmented target, the more inferiority of the segmented target has; (iii) while the number of the layers is fixed, e.g. double layers in the present test, the impact resistance of the segmented target is dependent on the order of the slabs, which is enhanced with the thickness of the later RC plate increasing. (3) An explicit dimensionless expression for predicting the terminal ballistic parameters of the projectile perforating the RC slab was proposed and well validated. (4) The newly proposed equivalent approach for predicting the ballistic limit of the projectile perforating RC/steel composite target was evaluated with the present tests.

EARTHQUAKE ANALYSIS ON 2D RC FRAMES WITH DIFFERENT ASPECT RATIOS OF MASONRY INFILL AND MONOLITHIC PANEL

RC structures are one of the most famous and most utilized types of construction throughout the world. The wall panels for this type of structures usually are made of masonry infill or monolithic RC panels. In this paper, earthquake analysis of a typical 2D-RC frame is carried out. Masonry infill is modeled as equivalent diagonal strut and monolithic panel is modeled as shell element. Modal analysis is carried out on the models and the results are compared with the shake table tests conducted at Central Power Research Institute (CPRI), Bangalore to validate the models. Earthquake analysis is continued with equivalent static, response spectrum and time history analyses for all the zones (II-V) as per IS: 1893(Part-1):2002. The analysis results such as natural frequency, displacement, interstorey drift and acceleration are tabulated, compared and conclusions are drawn.

Strength of connections in precast concrete structures

The available experimental and numerical results of many studies of behavior of reinforced concrete connections for different stages of loading, up to fracture loading, are presented and analyzed in this paper. The problem of beam-column connection (or plate-wall connection) in prefabricated monolithic structures is emphasized. Fracture mechanisms of RC structures, the theoretical basis for their analysis, and the use of fracture mechanics in RC structures were also considered, as well as the mathematical models of prefabricated connections. In order to formulate an adequate mathematical model for calculating the connections, the dominant parameters influencing the behaviour of these connections were analyzed. A failure model for the prefabricated wall - monolithic RC plate connection was formulated. In building the model, the results of implemented experimental and numerical research of prefabricated connection in the MMS system from 2007 were used. Experiences with the implementation of the aforementioned construction system in structures in Tuzla, in the 1980's last century, were additionally used. The proposed mathematical models provide a sufficiently accurate failure assessment of prefabricated reinforced concrete connections.

Debonding of FRP in bending: Simplified model and experimental validation

Reinforced concrete members strengthened in bending by bonding of surface-mounted fiber-reinforced polymer (FRP) may present several failure modes: failure of material (reinforcing steel, concrete and composite material) or failure of the interface between concrete-adhesive or adhesive-FRP. Nevertheless, experience gained from testing confirms that in most cases delamination prevails over the other possible rupture modes. Delamination in FRP strengthened sections is difficult to model because it involves multiple parameters such as FRP stiffness, adhesive material properties, presence of cracks in concrete, among others. A simplified model to predict strain of FRP at failure is presented in this paper. The experimental validation is presented as well. With this purpose carbon FRP and aramid strengthened specimens and large scale bridge models are considered. The types of bridge models tested include externally-prestressed segmental box-girder and monolithic RC continuous girders. Based on the results of the proposed model, an equation for the prediction of the ultimate force per unit width in the FRP to prevent FRP debonding is proposed. The equation has been experimentally checked with beams of small and large size, representative of real structures. In comparison to other available models, the equation is very simple to apply.

Monolithic RC All-Pass Networks with Constant-Phase-Difference Outputs

All-pass network techniques have made it possible to realize very small monolithic lumped active phase shifters with decade bandwidths, high yield, and relative phase stability, even when the device parameters vary +-20 percent. We have successfully demonstrated fully monolithic first-order networks (at 250 MHz) and second-order networks (at 4 GHz).

Monolithic RC all-pass networks with constant-phase-difference outputs

All-pass network techniques have made it possible to realize very small monolithic lumped active phase shifters with decade bandwidths, high yield, and relative phase stability, even when the device parameters vary ± 20 percent. We have successfully demonstrated fully monolithic first-order networks (at 250 MHz) and second-order networks (at 4 GHz).