Richard Henry

Understanding Poor Seismic Performance of Concrete Walls and Design Implications

The 2010–2011 Canterbury earthquakes in New Zealand revealed (1) improved structural response resulting from historical design advancements, (2) poor structural performance due to previously identified shortcomings that had been insufficiently addressed in design practice, and (3) new deficiencies that were not previously recognized because of premature failure resulting from other design flaws. This paper summarizes damage to concrete walls observed in the February 2011 Christchurch earthquake, proposes links between the observed response and specific design concerns, and offers suggestions for improving seismic design of walls in the following areas: amount of longitudinal reinforcement in wall end regions, suitable wall thickness to minimize the potential for out-of-plane buckling, and minimum vertical reinforcement requirements.

Concept and Finite-Element Modeling of New Steel Shear Connectors for Self-Centering Wall Systems

Self-centering precast concrete walls have been found to provide excellent seismic resistance. Such systems typically exhibit low energy dissipation, requiring supplementary dissipating components to improve their seismic performance. Mild steel shear connectors can provide an economical energy dissipating element. The design and analysis of steel shear connectors for a new precast wall system has been undertaken. A series of finite-element analyses were conducted to investigate the behavior of different types of connectors. Emerged from these analyses is a oval-shaped connector (O-connector) that provided satisfactory force-displacement behavior and appeared well suited for the new wall system in high seismic regions. An extensive experimental test program was then conducted to verify the performance of the chosen O-connector, which confirmed the expected response with sufficient energy dissipation. The experimental data demonstrated good correlation with the finite-element model developed, providing satisfactory confidence in the finite-element technique used for the development of the different connectors.

Cyclic Testing of Reinforced Concrete Walls with Distributed Minimum Vertical Reinforcement

AbstractDuring the 2010/2011 Canterbury earthquakes in New Zealand, several reinforced concrete (RC) walls in multistory buildings formed only a limited number of cracks at the wall base with a fra...

Modelling and experimental plan of reinforced concrete walls with minimum vertical reinforcement

During the 2010/2011 Canterbury earthquakes, several reinforced concrete (RC) walls in multistorey buildings formed a limited number of cracks at the wall base with fracture of vertical reinforcement occurring. This failure mode is typical of lightly reinforced concrete members, where the area of reinforcing steel is insufficient to develop the tension force required to form secondary cracks. The minimum vertical reinforcement limits for RC walls in different concrete design standards were compared, and a series of numerical analyses were used to investigate the behavior of an example RC wall designed according to the minimum requirements of each standard. The analysis results confirmed the observed failure mode of an RC wall with less than the current minimum vertical reinforcement that was damaged during the Canterbury earthquakes. Furthermore, RC walls built in accordance with current minimum vertical reinforcement requirements in both ACI 318-11 and NZS 3101:2006 are still susceptible to limited flexural cracking and premature bar fracture. The ductility of RC walls with concentrated reinforcement at the wall ends, such as that required by Eurocode 8, CSA 2004 and GB 50010, was significantly improved. A detailed investigation is currently underway to verify the seismic performance of lightly reinforced concrete walls and an experimental setup has been developed to subject RC wall specimen to loading that is representative of a multi-storey building. 1 PhD candidate, Dept. of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand, 1142 2 Lecturer, Dept. of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand, 1142 3 Lecturer, Dept. of Civil and Environmental Engineering, The University of Auckland, Auckland, New Zealand, 1142 Tenth U.S. National Conference on Earthquake Engineering Frontiers of Earthquake Engineering July 21-25, 2014 Anchorage, Alaska 10NCEE Modelling and Experimental Plan of Reinforced Concrete Walls with Minimum Vertical Reinforcement Y. Lu, R. S. Henry and Q. T. Ma

Signature Failure Modes of Pipelines Constructed of Different Materials When Subjected to Earthquakes

AbstractThe 2010/2011 Canterbury (New Zealand) earthquakes caused significant damage to buried pipeline infrastructure. Observations of damaged pipes that were made during either repair or replacement were used to define representative examples of the damage to each of the commonly used pipe materials. The different pipe materials that were considered included steel reinforced concrete, polyvinyl chloride, high-density polyethylene, cast iron, asbestos cement, and vitrified clay. Photographs of damaged pipes at the time of repair were collected and analyzed to identify pipe failure modes. It was determined that different pipeline materials exhibited different failure mechanisms during the earthquakes and that each pipe material was found to have a distinct failure signature. In particular, polyvinyl chloride pipes behaved in an unexpected brittle way. The failure mechanisms of each type of pipe are described using engineering nomenclature, and the signature failure modes are categorized and tabulated to f...

Testing support connections of 400 deep hollow-core precast concrete floors

The use of precast concrete flooring systems is widespread within New Zealand and there has been a significant amount of research undertaken in recent years to investigate their seismic performance. Support connections for precast concrete floor units are subjected to earthquake induced deformations, including a relative rotation between the unit and support beam and a pull-off effect caused by beam elongation. Based on previous testing, recommended support connection details for precast hollow-core floor units are given in NZS 3101:2006. However, the building code verification method (B1/VM1) limits the use of this recommended detail to hollow-core units with a depth of 300 mm or less. Hollow-core units with a depth of 400 mm (400HC) are currently being produced in New Zealand and experimental testing is required to verify the seismic performance of these 400HC units with existing support connection details. An experimental program was initiated to investigate the seismic performance of current support connection details for 400HC floor units. A test setup was developed to subject the hollow-core support connection to deformations simulating seismic actions in a building in addition to gravitational loading. The first two tests have been completed, and it was observed that the connection details provided an adequate level of performance under the application of seismic actions.

An experimental investigation of a wall-to-floor connector for self-centering walls

Previous research has shown that self-centering walls have excellent seismic performance. However, as uplift and rocking occur at the base of a self-centering wall, the floors would have to accommodate this uplift if they are rigidly connected to the wall. Consequently, the floors may be subjected to inelastic demands and associated damage, which can adversely affect the seismic response of the building. A series of experimental tests were conducted to investigate a new wall-to-floor connector that can isolate the floor from the wall’s relative uplift and rotation while transferring inertia forces from the floor to the wall. Individual connectors were subjected to pseudo-static cyclic tension or shear loading. Multiple connectors were utilised in a subassembly test that comprised of a third scale prototype wall and representative floor. The test results showed the connectors had satisfactory shear and tensile force-displacement behaviour. The connector elastically resisted forces greater than the suggested design strength resulting in a lateral deformation less than 2 mm at the suggested design strength. Based on the subassembly tests conducted so far the connectors were able to fully isolate the floor if the uplift at the connector location is limited to 25 mm. The connectors transferred lateral force from floor to wall for all loading and unloading cycles during testing.