Analytical Modelling of Jointed Precast Concrete Beam-to-Column Connections with Different Damping Systems

Jointed precast concrete systems typically have low inherent damping and are thus particularly suitable for applying supplemental damping systems. Analytical modelling is utilised to characterise jointed beam-to-column rocking connections, using a rate-dependent tri-linear compound version of the well-known Menegotto-Pinto rule. The analytical model is verified against near full-scale experimental results. The beam-column connections are constructed utilising Damage Avoidance Design (DAD) principles with unbonded post-tensioned tendons. High force-to-volume extrusion-based energy dissipaters are externally fitted to provide supplemental energy dissipation and modify joint hysteretic performance. Multiple joint configurations are analysed, with supplemental damping systems modified to investigate the effect of damping forces on joint hysteresis. Particular attention is given to the re-centring limit. Good agreement between the analytical models and experimental results is demonstrated, with discussion of possible improvements. Overall, system damping behaviour is significantly improved by adding the extrusion based damping system

Development of Microstrip Gas Chambers

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Incremental dynamic analysis applied to seismic financial risk assessment of bridges

Incremental dynamic analysis (IDA) is applied in a performance-based earthquake engineering context to investigate expected structural response, damage outcomes, and financial loss from highway bridges. This quantitative risk analysis procedure consists of: adopting a suitable suite of ground motions and performing IDA on a nonlinear model of the prototype structure; summarizing and parameterizing the IDA results into various percentile performance bounds; and integrating the results with respect to hazard intensity-recurrence relations into a probabilistic risk format. An illustrative example of the procedure is given for reinforced concrete highway bridge piers, designed to New Zealand, Japan and Caltrans specifications. It is shown that bridges designed to a "Design Basis Earthquake" that has a 10% probability in 50 years with PGA = 0.4 g, and detailed according to the specification of each country, should perform well without extensive damage. However, if a larger earthquake occurs, such as a maximum considered event which has a probability of 2% in 50 years, then extensive damage with the possibility of collapse may be expected. The financial implications of this vulnerability are also given, revealing a fourfold variation between the three countrie

Computational and rapid expected annual loss estimation methodologies for structures

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 insurers. A simplified method for estimating EAL without conducting time-consuming non-linear dynamic analyses is presented. Relationships between intensity measures and engineering demand parameters resulting from a pushover analysis and a modified capacity-spectrum method are combined with epistemic and aleatory uncertainties to arrive at a probabilistic demand model. Damage measures are established to determine thresholds for damage states from which loss ratios can be defined. Financial implications due to damage can then be quantified in the form of EAL by integrating total losses for all likely earthquake scenarios. This rapid loss estimation method is verified through the computationally intensive incremental dynamic analysis, with the results processed using a distribution-free methodology. To illustrate the application of the proposed method, the seismic vulnerability of two highway bridge piers is compared; one bridge is traditionally designed for ductility while the other is based on an emerging damage avoidance design (DAD) philosophy. The DAD pier is found to have a clear advantage over the conventional pier; the EAL of the DAD pier is less than 20% of its ductile counterpart. This is shown to be primarily due to its inherent damage-free behaviour for small to medium earthquake intensities, whose contribution to EAL is significantly more than that of very rare events

Quasi-Static Testing of a Damage Protected Beam-column Subassembly with Internal Lead Damping Devices

Multiple reversed cyclic quasi-static tests are performed on an 80 percent scale 3D beam column joint subassembly. The physical model is taken from an exterior connection of a jointed precast concrete frame prototype structure that is designed for damage avoidance. Unbonded post-tensioned prestress is provided by high-alloy high-strength threaded bars. Draped and straight tendon profiles are used in the transverse and orthogonal directions, respectively. The joint region is armoured to avoid damage by providing steel plates at the rocking edges of the beam-column interface. Supplemental energy dissipation is provided by high-performance lead-damping devices cast internally in each beam. A combination of couplers and cast in-situ closure pours at the beam ends are used to ensure reasonable construction tolerances. Column axial load and floor dead load are simulated. The global performance of the subassembly and the efficiency of the lead dampers is critically discussed. The subassembly had negligible residual displacements and minimal damage after the test. The hysteresis loops showed stable energy dissipation indicating the success of the dampers. Relatively simple hand methods of predicted performance are shown to conform to the observed experimental behaviour

High-Force-to-Volume Seismic Dissipators Embedded in a Jointed PreCast Concrete Frame

An experimental and computational study of an 80 percent scale precast concrete 3D beam-column joint subassembly designed with high force-to-volume (HF2V) dampers and damage-protected rocking connections is presented. A prestress system is implemented using high-alloy high-strength unbonded thread-bars through the beams and columns. The threadbars are post-tensioned and supplemental energy dissipation is provided by internally mounted lead-extrusion dampers. A multi-level seismic performance assessment (MSPA) is conducted considering three performance objectives related to occupant protection and collapse prevention. First, bi-directional quasi-static cyclic tests characterise the specimen‟s performance. Results are used in a 3D nonlinear incremental dynamic analysis (IDA), to select critical earthquakes for further bi-directional experimental tests. Thus, quasi-earthquake displacement tests are performed using the computationally predicted seismic demands corresponding to these ground motions. Resulting damage to the specimen is negligible, and the specimen satisfies all performance objectives related to serviceability, life-safety, and collapse prevention

Investigation of Rocking Connections Designed for Damage Avoidance with High Force-to-Volume Energy Dissipation

Modern structures are designed with a sacrificial design principle that values life safety at the expense of energy-absorbing structural damage. The significant long term economic impact of major seismic events due to the resulting structural damage demands a new generation of structures that can withstand large earthquakes with minimal or zero damage - while guaranteeing life safety. This research presents a new approach to damage avoidance design (DAD) connections that absorb significantly more seismic energy than sacrificially designed structures. The design approach utilizes hinged or rocking connections with energy absorption provided by small volume, high force (100-400kN) lead dampers designed to fit within standard structural connections. Proof of concept experimental results are presented for three connections, including: 1) 3D exterior post-tensioned RC connection; 2) corner post-tensioned RC connection; and 3) 2D exterior steel connection. Experiments are conducted on scaled specimens which are subjected to repeated reversed cycles of seismic drifts from 0.5-4.0% in increments of 0.5-1.0%. The high force-to-volume (HF2V) dampers reliably provide over 20% more damping than other systems – and do so on every motion cycle. It is therefore concluded that this novel DAD connection can provide sustained superior energy dissipation without damage

Performance of a damage-protected beam-column subassembly utilizing external HF2V energy dissipation devices

Ductile-jointed connections, which generally require some form of supplementary energy dissipation to alleviate displacement response, typically employ mild steel energy dissipation devices. These devices run the risk of low-cycle fatigue, are effective only for peak cycles that exceed prior displacements, are prone to buckling, and may require replacement following an earthquake. This study presents an experimental investigation employing an alternative to mild steel: a high force-to-volume (HF2V) class of damper-based energy dissipation devices. Tests are performed on a near full-scale beam–column joint subassembly utilizing externally mounted compact HF2V devices. Two configurations are considered: an exterior joint with two seismic beams and one gravity beam framing into a central column, and a corner joint with only one seismic beam and one gravity beam framing into a column. Quasi-static tests are performed to column drifts up to 4%. The experiments validate the efficacy of the HF2V device concept, demonstrating good hysteretic energy dissipation, and minimal residual device force, allowing ready re-centring of the joint. The devices dissipate energy consistently on every cycle without the deterioration observed in the yielding steel bar type of devices. The effectiveness of the HF2V devices on structural hysteretic behavior is noted to be sensitive to the relative stiffness of the anchoring elements, indicating that better efficiency would be obtained in an embedded design

Multi-level Seismic Performance Assessment of a Damage Protected Beam-column Joint with Internal Lead Dampers

A multi-level seismic performance assessment is performed on a near full scale beam-column subassembly. The physical model is taken from a 3D exterior connection of a jointed precast concrete frame structure that is designed for damage avoidance. Unbonded post-tensioned prestress is provided by high-alloy high-strength thread-bars. Draped and straight tendon profiles are used in the transverse and orthogonal directions, respectively. The joint region is armoured to avoid damage by providing steel plates at the beam-column contact points. Supplemental energy dissipation is provided by high-performance lead-damping devices cast internally in each beam. Bi-directional quasi-earthquake displacement profiles are applied meaning the input displacement profiles are taken directly from the results of inelastic dynamic analysis. Three input earthquakes are selected probabilistically to represent multiple levels of seismic demand. Results from physical testing are critically discussed