Keynote Address Learning from Hawke's Bay 1931 Earthquake Performance Assessment and Retrofit Decision Making for Risk Mitigation Behaviour of Walls and Piers Understanding Reinforced Concrete Behaviour Modelling Earthquake Performance Earthquake Performance Poster Papers Design and Development 

The Analysis of Reinforced Concrete Rocking Wall Behaviour

Mark Browne, Athol Carr and Des Bull

The behaviour of rocking walls is investigated using the time history analysis program Ruaumoko (2005). The advantages of allowing a wall to rock on its foundations are analysed and found to be significant. The Ultimate, Serviceability and Survival Limit States are all included in the analysis to view the advantage of the rocking system at each of the intensities of loading. The moments, shear forces and accelerations are all found to be significantly reduced in the rocking wall when compared to a wall fixed at the base. The displacement at the top of the wall is mainly caused by the rotation at the base of the wall. These displacements are found to be low enough so as to not interfere with other buildings during a seismic event. The drift is also investigated and found to be low. The rocking should therefore not significantly affect the behaviour of other components attached to the wall. The disadvantage of rocking is the lack of energy dissipation. The uplift at the base of the wall is found to be low enough to allow for energy dissipation devices to be attached to the base to increase the energy dissipation of the system. The natural period of free vibration of the wall, on average, increases by a factor of three during the largest rocking excursions. This reduces the base shear transmitted into the wall.

Paper P15: [Read]

An Alternative Mathematical Model for a Controlled Rocking System

Quincy Ma, John Butterworth and Barry Davidson

A new mathematical model for representing a controlled rocking system is presented in a non dimensional format. The model permits a universal rocking wall to be established, and its dynamic behaviour under sinusoidal base excitation to be subsequently analysed. Preliminary equations for predicting the peak possible response of the system, based on exploiting features of the mathematical functions in the universal rocking system’s governing differential equation, are proposed. Validity of the preliminary equations is demonstrated by means of a series of time-history analyses.

Paper P16: [Read]

Probabilistic Analysis of Rocking Blocks

Mohamed ElGawady, Quincy Ma, John Butterworth and Jason Ingham

The rocking response of rigid blocks with an aspect ratio of 5 was investigated, with particular focus on the possible effects of interface materials. The blocks were allowed to rock on timber, steel, reinforced concrete, and rubber bases. Preliminary results showed that the interface material exerted a significant influence on the rocking response. The rubber base exhibited the lowest coefficient of restitution, followed by steel, timber, and concrete. In addition, the rocking characteristics of the blocks were calculated using simple mathematical models based on fundamental principles of mechanics. The models were generally found to overestimate the rotation amplitudes and periods due to inaccuracy in estimating the coefficient of restitution. The measured coefficients of restitution were approximately 0.95 and 0.67 of the predicted values for concrete and rubber bases, respectively.

Paper P17: [Read]

Hybrid Experimental Analysis of Semi-active Rocking Wall Systems

Kerry Mulligan, Maxime Fougere, John Mander, Geoff Chase, Bruce Deam, Guillaume Danton and Rodney Elliot

Rocking walls are an effective method of dissipating seismic response energy and mitigating damage. Semi-active resetable devices have shown significant potential to dissipate energy, customize hysteretic behavior and reduce damage. Hence, the addition of a resetable device within a rocking wall can further improve the overall energy management during seismic events. A scaled semi-active rocking wall system, designed for a large open structure, is analysed using real-time, high-speed hybrid testing. The semi-active devices are controlled to provide supplementary resistance only for the upward rocking motion of the wall, providing semi-active energy dissipation over half of each cycle and relying on radiation damping for the other half. An validated model of the semi-active devices is used to examine the response of a full scale rocking wall system to a suite of earthquake ground motions to prove the overall concept. Overall, similar semi-active rocking walls could also be used as supplemental, low-footprint response energy management systems in retrofitting a variety of structures.

Paper P18: [Read]

Experimental Validation of High-performance Hybrid Bridge Piers

Dion Marriott, Alistair Boys, Stefano Pampanin and Alessandro Palermo

An appreciation of the crucial need for a high level of performance from reinforced concrete structures located in seismically active regions has been extensively recognised in the past decade. Appropriate performance-based criteria are essential in ensuring the desired behaviour of structures, especially when a low level of post-earthquake damage is desired.

“Hybrid” jointed ductile connections originally developed for either pre-cast concrete frames and wall systems have been shown to exhibit superior performance complemented with a reduced level of damage and negligible residual deformations of the structural systems. These innovative advanced systems, consisting of relatively simple construction methods (based on post-tensioning techniques), have been recently proposed to be adopted in bridge piers and systems as a viable and highly competitive alternative to traditional monolithic cast-in-place construction.

Paper P19: [Read]

Financial Seismic Risk Assessment of RC Bridge Piers using a Distribution-free Approach

Kevin Solberg, John Mander and Rajesh Dhakal

Expected annual loss (EAL), which can be expressed in dollars, is an effective way of communicating the seismic vulnerability of constructed facilities to owners and decision makers. A concise method for computing EAL without the inherent bias of requiring a specific analytical probability distribution is presented. The relationships between intensity measures and engineering demand parameters resulting from an Incremental Dynamic Analysis are sorted into fractal intervals by way of spectral reordering and modified to incorporate additional sources of uncertainty and randomness. Damage measures are defined to determine thresholds for damage states. Damage is quantified by loss ratios defined as repair cost divided by replacement cost. The results are numerically integrated to give EAL. An example illustrating the method is performed, comparing the seismic vulnerability of two highway bridge piers; one pier traditionally designed for ductility, and the other designed for damage avoidance. The damage avoidance pier has a clear advantage over the conventional pier, with an EAL some 85% less than its ductile counterpart. This is shown to be primarily due to its inherent damage-free behaviour for almost all ground motions, except for very rare events that could potentially lead to toppling.

Paper P20: [Read]

Keynote Address Learning from Hawke's Bay 1931 Earthquake Performance Assessment and Retrofit Decision Making for Risk Mitigation Behaviour of Walls and Piers Understanding Reinforced Concrete Behaviour Modelling Earthquake Performance Earthquake Performance Poster Papers Design and Development