164 results for Dhakal, R.P.

  • Ceiling systems design and installation lessons from the Canterbury Earthquakes

    Dhakal, R.P.; MacRae, G. (2013)


    University of Canterbury Library

    Damage to ceiling systems resulted in a substantial financial loss to building owners in the Canterbury earthquakes. In some buildings, collapse of ceilings could easily have resulted in severe injury to occupants. This paper summarizes the types of ceiling damage observed in the Canterbury earthquakes, and draws useful lessons from the observed performance of different types of ceiling systems. Existing ceiling manufacturing and installing practices/regulations in New Zealand are critically scrutinized to identify deficiencies, and measures are suggested to improve the practice so that the damage to ceilings and the resulting loss are minimized in future earthquakes.

    View record details
  • Nonlinear Analysis of Laterally Loaded Reinforced Concrete Piles

    Dhakal, R.P.; Salem, Hamed; Maekawa, K. (1999)


    University of Canterbury Library

    Reinforced concrete piles embedded in homogeneous sandy soil were analyzed using a three-dimensional nonlinear finite element program, COM3, developed in Concrete Laboratory, The University of Tokyo. Nonlinear space frame element was used for the modeling of reinforced concrete piles. The applicability of the models was checked by comparing the analytical results with the experimental ones. It was found that the analysis was able to predict the behavior for general cases, but in the case of large deformation, the analysis underestimated the inelastic axial deformation. The difference of the analytical and experimental results was thought to be caused by the spalling of cover concrete and buckling of reinforcing bars. Hence, both cover concrete spalling and reinforcement buckling were modeled and included in COM3. Significant qualitative improvement was observed in the inelastic axial deformation al behavior of the RC piles.

    View record details
  • Influence Of HF2V Damping Devices On The Performance Of The SAC3 Building Subjected To The SAC Ground Motion Suites

    Rodgers, G.W.; Chase, J.G.; MacRae, G.A.; Bacht, T.; Dhakal, R.P.; Desombre, J. (2010)


    University of Canterbury Library

    Recent advances in energy dissipation for structural systems can create structural connections that undergo zero sacrificial energy absorbing damage, even at extreme story drifts. However, questions exist around the ability of such structures to re-center after a major event. In this paper, the seismic performance of the as-designed SAC LA3 seismic frame with rigid moment connections at the beam ends is compared with the same frame using semi-rigid connections with high force-to-volume (HF2V) lead dissipators. Non-linear dynamic analysis is preformed using Abaqus™. With respect to re-centering, the presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of gravity frames, caused a 12% increase in period due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey drift ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The addition of braces with a stiffness 20% of the pushover stiffness ensures that the structures can re-center after any given event to within construction error. The realistic non-linear dynamic analyses combining HF2V dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.

    View record details
  • Finite Element Modelling of Precast Hollow-Core Concrete Floors Under Fire Conditions

    Chang, J.; Dhakal, R.P.; Moss, P.J.; Buchanan, A.H. (2008)


    University of Canterbury Library

    Precast prestressed hollow-core concrete flooring units are widely used in reinforced concrete moment-resisting frame buildings in New Zealand, yet their behaviour under fire has not received much attention. This is because large scale fire tests are difficult and expensive, leaving computer analysis as the only alternative. However, the currently available computer analysis methods are neither accurate nor easy to use. This paper describes a simple yet reliable computational method to be used in design for modelling the structural behaviour of hollow-core prestressed concrete slabs exposed to fires. The model has a major limitation of not being able to model shear or tensile failure in the webs of the hollow-core units, but the simulation outcomes show reasonably good agreement with experimental fire tests of hollow-core slab units, thereby verifying the reliability of the model.

    View record details
  • Modelling the fire resistance of prestressed concrete floors using multi-spring connection elements

    Min, J.K.; Moss, P.J.; Dhakal, R.P.; Buchanan, A.H. (2010)


    University of Canterbury Library

    Despite big advances in analytical modelling of the performance of structures exposed to fire, there has been difficulty in modelling the fire performance of precast prestressed concrete floor slabs in multi storey buildings. The fire resistance of these floor systems is heavily influenced by the end connections and the stiffness of the surrounding structure, both of which must be considered in any analysis. Previous “traditional” studies have modelled the floor slabs with beam or shell elements in which the end nodes share the nodes of the beam elements representing the supporting beams. This is acceptable for cast-in-situ or precast flooring system without prestressing, but leads to a major problem for precast prestressed flooring systems where the steel tendons terminate at the end of the flooring units, because the approach of sharing nodes of the supporting beam and floor assumes that these tendons are anchored into the supporting beams. In order to solve this problem, a “multi-spring” connection element has been developed. The multi-spring connection element consists of several parallel axial springs sandwiched between two rigid plates. Each spring represents either a steel reinforcing layer or a segment of concrete in the floor cross-section. The concrete springs have compression-only properties. This multi-spring connection is placed between the end nodes of the floor and the nodes of the supporting beam. With this element, it is possible to terminate the prestressing tendons at the end node of the floor elements and to anchor only the topping reinforcement into the supporting systems predicted using the traditional approach and the newly developed multispring connection, with applications to different forms of precast concrete floors in multi storey buildings.

    View record details
  • Joint Contribution to the Deformation of RC Beam-Column Sub-Assemblies

    Dhakal, R.P.; Pan, T.C. (2004)


    University of Canterbury Library

    In this paper, the contribution of joint shear deformation to the overall storey-drift of reinforced concrete (RC) beam-column sub-assemblies is investigated experimentally. Two lightly reinforced beamcolumn sub-assemblies, one without any hoops inside the joint core and the other with hoops significantly less than that required by the incumbent seismic design codes, were tested under a constant axial compression and gradually increasing reversed cyclic displacements. Both specimens experienced severe damage in the joint due to excessive shear deformation of the joint core. Unlike in seismically designed ductile frames, joint shear deformation accounted for more than 50% of the overall storey-drift in the tested specimens. Comparison of the two test results showed that a small amount of hoops in the joint core, though not enough to satisfy seismic requirements, helps to confine the joint core and to inhibit the joint shear deformation to some extent.

    View record details
  • Cyclic beam bending test for assessment of bond-slip behavior

    Soleymani Ashtiani, M.; Dhakal, R.P.; Scott, A.N.; Bull, D.K. (2012)


    University of Canterbury Library

    Bond between reinforcement and concrete is one of the most important aspects in structural response of reinforced concrete (RC) members. Basic RC theories assume compatibility of strains between concrete and steel which is valid only if a perfect bond exists between the two materials. Therefore investigating bond properties under different loading conditions and considering various variables is of great importance. Although researchers have extensively explored bond-slip relationships for different concrete and steel types under monotonic loading using different test setups, less is reported on bond properties under reversed cyclic loading. Modified pullout tests have previously been used to investigate cyclic bond-slip relationships; nevertheless these tests do not represent the actual bond behaviour inside RC members subjected to flexural actions. This study focuses on developing a specific test setup and designing a beam specimen for cyclic bond test following RILEM recommendations for monotonic assessment of bond properties, which require a two-point loading (four-point bending) setup. The main challenge was to design a stable cyclic test setup in order to ensure no additional forces generated in the system during the test. High strength self-compacting concrete (HSSCC) beam specimens were chosen for the test; the beam specimens were designed in such a way that they could withstand load reversals.

    View record details
  • Seismic sustainability assessment of structural systems: Frame or wall structures?

    Yeow, T.; MacRae, G.A.; Dhakal, R.P.; Bradley, B.A. (2012)


    University of Canterbury Library

    A preliminary case study assessing the seismic sustainability of two reinforced concrete structures, a frame structure and a wall structure, was conducted to determine which structural system is more seismically sustainable. The two structures were designed to the same standards and were assumed to be located in Christchurch, New Zealand. A component-based probabilistic seismic loss assessment, considering direct losses only, was conducted for two ground motion records, regarded to approximately represent a 1 in 500 year earthquake event and a 1 in 2500 year earthquake event, respectively. It is shown that the wall structure results in lower direct losses than the frame structure in the less severe ground motion scenario. However, in the more severe ground motion scenario, the frame structure results in lower direct losses. Hence, this study demonstrates that which structural system has the lower direct losses depends on the ground motion intensity level.

    View record details
  • Influence Of HF2V Damping Devices On The Performance Of The SAC3 Building Subjected To The SAC Ground Motion Suites

    Rodgers, G.W.; Chase, J.G.; MacRae, G.A.; Bacht, T.; Dhakal, R.P.; Desombre, J. (2010)


    University of Canterbury Library

    Recent advances in energy dissipation for structural systems can create structural connections that undergo zero sacrificial energy absorbing damage, even at extreme story drifts. However, questions exist around the ability of such structures to re-center after a major event. In this paper, the seismic performance of the as-designed SAC LA3 seismic frame with rigid moment connections at the beam ends is compared with the same frame using semi-rigid connections with high force-to-volume (HF2V) lead dissipators. Non-linear dynamic analysis is preformed using Abaqus™. With respect to re-centering, the presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of gravity frames, caused a 12% increase in period due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey drift ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The addition of braces with a stiffness 20% of the pushover stiffness ensures that the structures can re-center after any given event to within construction error. The realistic non-linear dynamic analyses combining HF2V lead dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.

    View record details
  • Seismic performance of high-strength self-compacting-concrete in reinforced concrete beam column joints

    Ashtiani, M.S.; Dhakal, R.P.; Scott, A. (2012)


    University of Canterbury Library

    Beam-column joints of reinforced concrete building frames play an important role under seismic excitations. These are one of the most congested areas in reinforced concrete framed structures; placement of concrete and proper compaction in such areas are hence substantially challenging. This offers a unique area of application for self-compacting concrete which can flow through every corner of extensively reinforced area without any vibration. Therefore if implementing self-compacting concrete in beam-column joints does not compromise seismic performance of the frame, it can be used instead of conventional concrete. This paper focuses on implementation of high-strength self-compacting concrete in beam-column joints and assessment of its seismic behaviour under reversed cyclic loading. Three interior beam-column subassemblies chosen to vary in concrete type and compressive strength are designed as per the New Zealand Standard NZ3101:2006. The specimens are instrumented to measure the load, displacement/drift, ductility, joint shear deformations, and elongation of the plastic hinge zone. The cracking pattern at different load levels and the mode of failure are also recorded and compared among different specimens.

    View record details
  • Preliminary experimental verification of current content sliding modelling techniques

    Yeow, T.Z.; MacRae, G.A.; Dhakal, R.P.; Bradley, B.A. (2014)


    University of Canterbury Library

    Most analytical studies focusing on the sliding of building contents usually make an assumption that the friction force-sliding displacement behaviour is elasto-plastic (e.g. friction coefficient remains constant during sliding). This preliminary study uses experimental data to verify if this assumption is reasonable. Shake table tests of a desk on common flooring materials were conducted to investigate the factors influencing friction behaviour, and to observe the behaviour of the contents under sinusoidal motion. Up to a 15% decrease in friction coefficient was observed with either an 80% increase in mass or a 20 times decrease in relative velocity, indicating that the friction coefficient is dependent on these two parameters. A comparison of the experimental and analytical sliding response of the desk under a single sinusoidal loading pattern on carpet flooring was conducted. Results show that the displacement amplitude of a single sliding excursion and the general sliding trend is well approximated using the elasto-plastic assumption. As such, despite the dependence of friction coefficient on sliding mass and velocity, the elasto-plastic behaviour assumption appears to be reasonable for the sinusoidal loading pattern examined in this paper.

    View record details
  • Using high-strength self-compacting concrete in reinforced concrete beam-column joints

    Soleymani Ashtiani, Mohammad; Dhakal, R.P.; Scott, A.N. (2013)


    University of Canterbury Library

    The capability of self-compacting concrete (SCC) in flowing through and filling in even the most congested areas makes it ideal for being used in congested reinforced concrete (RC) structural members such as beam-column joints (BCJ). However, members of tall multi-storey structures impose high capacity requirements where implementing normal-strength self-compacting concrete is not preferable. In the present study, a commercially reproducible high-strength self-compacting concrete (HSSCC), a conventionally vibrated high-strength concrete (CVHSC) and a normal strength conventionally vibrated concrete (CVC) were designed using locally available materials in Christchurch, New Zealand. Following the guidelines of the New Zealand concrete standards NZS3101, seven beam-column joints (BCJ) were designed. Factors such as the concrete type, grade of reinforcement, amount of joint shear stirrups, axial load, and direction of casting were considered variables. All BCJs were tested under a displacement-controlled quasi-static reversed cyclic regime. The cracking pattern at different load levels and the mode of failure were also recorded. In addition, the load, displacement, drift, ductility, joint shear deformations, and elongation of the plastic hinge zone were also measured during the experiment. It was found that not only none of the seismically important features were compromised by using HSSCC, but also the quality of material and ease of construction boosted the performance of the BCJs.

    View record details
  • Contents Sliding Response Spectra

    Lin, S.L.; MacRae, G.A.; Dhakal, R.P.; Yeow, T.Z. (2012)


    University of Canterbury Library

    Building content damage can cause significant economic loss in major earthquakes. This paper quantifies the contents damage to structures with similar backbone hysteresis curves, but with different unloading and reloading characteristics under both impulse and earthquake excitations scaled to the design level for Wellington. These sliding demands are expressed in terms of sliding spectra and they show that the amount of sliding depends on the shape of the hysteresis curve used. Two simple explanations are proposed and evaluated to determine which hysteresis loops would result in the greatest sliding damage. It is shown that a sudden increase in stiffness when the structure is moving at a high velocity is not the key factor. Instead, the velocity at the time of sliding initiation seems to correlate better with the calculated sliding distance.

    View record details
  • Choice of in-structure damping model: Do we have an answer?

    Puthanpurayil, A.; Dhakal, R.P.; Carr, A.J. (2012)


    University of Canterbury Library

    Recent researches have shown that the optimal distribution of dampers is sensitive to the choice of the in-structure damping models. Common practice is to use the classical viscous damping model originated by Rayleigh, through his famous „Rayleigh dissipation function‟. The main advantage of this model is that the orthogonality of the modes is preserved; thereby rendering the classical modal analysis for undamped vibration readily applicable to damped vibration as well. In a controlled frame, addition of external dampers makes the damping non-classical and the orthogonality of modes no longer exists. So use of the classical in-structure damping model (Rayleigh model) for controlled frames is not convincing and no justification is provided in the literature for the choice of this damping model. In this paper, the effect of choice of the damping models on the optimal distribution of dampers is investigated. It is observed that the optimal distribution of dampers could change based on the choice of the damping models. The results raise a huge concern regarding the realism of the optimality criterion achieved in terms of response reduction when a particular damping model is assumed with no specific justification.

    View record details
  • Cyclic beam bending test for assessment of bond-clip behavior

    Ashtiani, M.S.; Dhakal, R.P.; Scott, A.; Bull, D.K. (2012)


    University of Canterbury Library

    Bond between reinforcement and concrete is one of the most important aspects in structural response of reinforced concrete (RC) members. Basic RC theories assume compatibility of strains between concrete and steel which is valid only if a perfect bond exists between the two materials. Therefore investigating bond properties under different loading conditions and considering various variables is of great importance. Although researchers have extensively explored bond-slip relationships for different concrete and steel types under monotonic loading using different test setups, less is reported on bond properties under reversed cyclic loading. Modified pullout tests have previously been used to investigate cyclic bond-slip relationships; nevertheless these tests do not represent the actual bond behaviour inside RC members subjected to flexural actions. This study focuses on developing a specific test setup and designing a beam specimen for cyclic bond test following RILEM recommendations for monotonic assessment of bond properties, which require a two-point loading (four-point bending) setup. The main challenge was to design a stable cyclic test setup in order to ensure no additional forces generated in the system during the test. High strength self-compacting concrete (HSSCC) beam specimens were chosen for the test; the beam specimens were designed in such a way that they could withstand load reversals.

    View record details
  • Assessment of collapse capacity of RC buildings based on fiber-element modelling

    Ebrahami-Koopaee, M.; Dhakal, R.P.; Bradley, B.A.; MacRae, G.A. (2013)


    University of Canterbury Library

    Despite the fact that structural collapse is a key contributor to seismic risk, robust procedures for the assessment of structural collapse are typically absent in seismic design documents. This paper discusses probabilistic collapse capacity assessment of reinforced concrete buildings using the New Zealand red book building as a case study. Load resisting elements of RC buildings are traditionally modelled using lumped plasticity elements at predefined plastic hinge locations which require crude approximations of several features of post-peak response, which is very important in simulating structural collapse. This paper presents a discussion on the use of fiber-based nonlinear modelling, which utilizes generic path-dependent cyclic stress-strain relationships of concrete and reinforcing steel, for prediction of RC frame building collapse. A collapse capacity distribution accounting for ground motion uncertainty is estimated using a suite of ground motions and conducting incremental dynamic analysis (IDA), i.e., gradually increasing the intensity of the ground motions until the occurrence of collapse. It is shown that the fiber model simulates the collapse mechanism of the building without the upfront assumptions required in lumped plasticity modelling; thereby making the prediction more reliable.

    View record details
  • Building pounding damage observed in the 2011 Christchurch earthquake

    Cole, G.; Dhakal, R.P.; Chouw, N. (2012)


    University of Canterbury Library

    This paper describes the pounding damage sustained by buildings in the February 2011 Christchurch earthquake. Approximately 6% of buildings in Christchurch CBD were observed to have suffered some form of serious pounding damage. Typical and exceptional examples of building pounding damage are presented and discussed. Almost all building pounding damage occurred in unreinforced masonry buildings, highlighting their vulnerability to this phenomenon. Modern buildings were found to be vulnerable to pounding damage where overly stiff and strong ‘flashing’ components were installed in existing building separations. Soil variability is identified as a key aspect that amplifies the relative movement of buildings, and hence increases the likelihood of pounding damage. Building pounding damage is compared to the predicted critical pounding weaknesses that have been identified in previous analytical research.

    View record details
  • Seismic performance of high-strength self-compacting concrete in reinforced concrete beam-column joints

    Soleymani Ashtiani, M.; Dhakal, R.P.; Scott, A. N. (2012)


    University of Canterbury Library

    Beam-column joints of reinforced concrete building frames play an important role under seismic excitations. These are one of the most congested areas in reinforced concrete framed structures; placement of concrete and proper compaction in such areas are hence substantially challenging. This offers a unique area of application for self-compacting concrete which can flow through every corner of extensively reinforced area without any vibration. Therefore if implementing self-compacting concrete in beam-column joints does not compromise seismic performance of the frame, it can be used instead of conventional concrete. This paper focuses on implementation of high-strength self-compacting concrete in beam-column joints and assessment of its seismic behaviour under reversed cyclic loading. Three interior beam-column subassemblies chosen to vary in concrete type and compressive strength are designed as per the New Zealand Standard NZ3101:2006. The specimens are instrumented to measure the load, displacement/drift, ductility, joint shear deformations, and elongation of the plastic hinge zone. The cracking pattern at different load levels and the mode of failure are also recorded and compared among different specimens.

    View record details
  • Using High-Strength Self-Compacting Concrete in Reinforced Concrete Beam-Column Joints

    Soleymani Ashtiani, M.; Dhakal, R.P.; Scott, A.N. (2013)


    University of Canterbury Library

    The capability of self-compacting concrete (SCC) in flowing through and filling in even the most congested areas makes it ideal for being used in congested reinforced concrete (RC) structural members such as beam-column joints (BCJ). However, members of tall multi-storey structures impose high capacity requirements where implementing normal-strength self-compacting concrete is not preferable. In the present study, a commercially reproducible high-strength self-compacting concrete (HSSCC), a conventionally vibrated high-strength concrete (CVHSC) and a normal strength conventionally vibrated concrete (CVC) were designed using locally available materials in Christchurch, New Zealand. Following the guidelines of the New Zealand concrete standards NZS3101, seven beam-column joints (BCJ) were designed. Factors such as the concrete type, grade of reinforcement, amount of joint shear stirrups, axial load, and direction of casting were considered variables. All BCJs were tested under a displacement-controlled quasi-static reversed cyclic regime. The cracking pattern at different load levels and the mode of failure were also recorded. In addition, the load, displacement, drift, ductility, joint shear deformations, and elongation of the plastic hinge zone were also measured during the experiment. It was found that not only none of the seismically important features were compromised by using HSSCC, but also the quality of material and ease of construction boosted the performance of the BCJs.

    View record details
  • Qualitative Assessment of Structural Damage due to Underground Explosion

    Dhakal, R.P.; Pan, T.C.; Lan, S. (2001)


    University of Canterbury Library

    This paper investigates numerically the response of a reinforced concrete frame to explosion-induced ground motions simulated at different distances from the explosion source. The results indicate that nearby structures might experience sudden shear failure and distant structures might undergo less severe damage due to high frequency response that causes larger strain in spite of smaller displacement.

    View record details