John B. Mander

The Seismic Response of a 1:3 Scale Model R.C. Structure with Elastomeric Spring Dampers

In this experimental study, elastomeric spring dampers, which have a distinct re-centering characteristic, are used to retrofit a non-ductile, previously damaged 1/3 scale model reinforced concrete building frame structure which is subjected to a variety of ground motions in shaking table tests. A velocity dependent analytical model is developed and verified for the elastomeric spring dampers. This model is implemented in the widely available non-linear dynamic time history analysis computer program DRAIN-2DX to produce response predictions which are in good agreement with experimental observations. The elastomeric spring damper devices significantly attenuate the seismic response of the structure and provide a considerable amount of energy dissipation while the main non-ductile reinforced concrete structural load carrying elements remain elastic. The effect of varying the damper configuration on the structural response was also investigated.

Shake-Table Tests of Confined-Masonry Rocking Walls with Supplementary Hysteretic Damping

A shake-table investigation is conducted on a 40% scale model frame-wall system to validate the concept of rocking walls as primary seismic systems. The rocking wall concept was implemented on confined masonry walls, but the findings can be extended to any rocking wall system. As the inherent damping of this system is low, a pair of supplemental steel hysteretic energy dissipating dampers is used at the base of the wall. It is concluded that with careful detailing, damage is not only eliminated but the structure re-centers itself following a large earthquake.

Damage Avoidance Design Steel Beam-Column Moment Connection Using High-Force-to-Volume Dissipators

Existing welded steel moment frames are designed to tolerate substantial yielding and plastic rotation under earthquake loads. This sacrificial design approach can lead to permanent, and often irreparable damage when interstory drifts exceed 2%. The experimental seismic performance of a 50% full-scale damage avoidance designed structural steel beam-column connection is presented. The beam-column joint region consists of a top flange-hung beam connected to the column by an angle bracket. High-force-to-volume (HF2V) devices are attached from the column to the beam to provide joint rigidity and energy dissipation as the joint opens and closes. The HF2V devices are connected either below the beam flange or concealed above the beams lower flange. Reversed cyclic lateral load tests are conducted with drift amplitudes up to 4%. No damage is observed in the principal beam and column structural elements. The need for stiff device connections to achieve optimal device performance is demonstrated, and potential design solutions presented. Stable hysteresis and repeatable energy dissipation for a large number of cycles up to the 4% drift level is observed. It is concluded that superior and repeatable energy dissipation without damage can be achieved for every dynamic motion cycle, in contrast to conventional sacrificially designed welded moment frame connections.

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 thread-bars are posttensioned and supplemental energy dissipation is provided by internally mounted lead-extrusion dampers. A multilevel seismic performance assessment (MSPA) is conducted considering three performance objectives related to occupant protection and collapse prevention. First, bidirectional 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 bidirectional experimental tests. Thus, quasi-earthquake displacement tests are performed by using the computationally predicted seismic demands corresponding to these ground motions. Resulting ...

Seismic Performance of Damage-Protected Beam-Column Joints

This paper presents an experimental and computational study on the bidirectional behavior of a precast concrete three-dimensional (3D) beam-column joint subassembly designed with damage-protected rocking connections. A prestress system is implemented in which high-alloy, high-strength, unbonded threaded bars running through the beams are coupled to rods within the columns. The threaded bars are posttensioned and supplemental energy dissipation devices are also installed. Both wet and dry joint solutions are considered. The authors conducted a multilevel seismic performance assessment considering three performance objectives related to immediate occupancy and collapse prevention. First, bidirectional quasistatic cyclic tests were conducted and the specimen’s performance was characterized. This data was then used in a 3D nonlinear incremental dynamic analysis (IDA). Results from the IDA were used to select three critical earthquakes for further experimental bidirectional testing. Thus, quasi-earthquake displacement tests were performed. Results indicate the tested specimen met all 3 seismic performance objectives. In precast rocking frames designed to damage-avoidance principles, a cast-in-place closure pour at one beam end helps to alleviate construction tolerance issues and ensures the face of the beam is aligned properly with the column. The performance of such joints was found to be satisfactory.

Text vs. images: on the viability of social media to assess earthquake damage

In this paper, we investigate the potential of social media to provide rapid insights into the location and extent of damage associated with two recent earthquakes - the 2011 Tohoku earthquake in Japan and the 2011 Christchurch earthquake in New Zealand. Concretely, we (i) assess and model the spatial coverage of social media; and (ii) study the density and dynamics of social media in the aftermath of these two earthquakes. We examine the difference between text tweets and media tweets (containing links to images and videos), and investigate tweet density, re-tweet density, and user tweeting count to estimate the epicenter and to model the intensity attenuation of each earthquake. We find that media tweets provide more valuable location information, and that the relationship between social media activity vs. loss/damage attenuation suggests that social media following a catastrophic event can provide rapid insight into the extent of damage.

Compatibility Strut-and-Tie Modeling: Part I—Formulation

A compatibility-based strut-and-tie model (C-STM) intended for analyzing the nonlinear force-deformation behavior of disturbed regions and structural concrete deep beams is presented. In addition to the normal strut-and-tie force equilibrium requirements, the proposed C-STM accounts for nonlinear behavior using nonlinear constitutive relations for cracked reinforced concrete. The model is implemented using commercially available structural analysis software, SAP2000. To assess C-STM accuracy, convergence studies using different truss representations are explored. Particular emphasis is placed on investigating the behavior of deep cantilevered beams to provide insight into the progression of nonlinear response leading to the ultimate shear failure. New developments for modeling the nonlinear behavior of concrete compression chord members and compression-softening effects of diagonal concrete struts are proposed. The implementation is presented in the companion paper.

Market-implied spread for earthquake CAT bonds: financial implications of engineering decisions.

In the event of natural and man-made disasters, owners of large-scale infrastructure facilities (assets) need contingency plans to effectively restore the operations within the acceptable timescales. Traditionally, the insurance sector provides the coverage against potential losses. However, there are many problems associated with this traditional approach to risk transfer including counterparty risk and litigation. Recently, a number of innovative risk mitigation methods, termed alternative risk transfer (ART) methods, have been introduced to address these problems. One of the most important ART methods is catastrophe (CAT) bonds. The objective of this article is to develop an integrative model that links engineering design parameters with financial indicators including spread and bond rating. The developed framework is based on a four-step structural loss model and transformed survival model to determine expected excess returns. We illustrate the framework for a seismically designed bridge using two unique CAT bond contracts. The results show a nonlinear relationship between engineering design parameters and market-implied spread.

Compatibility Strut-and-Tie Modeling: Part II—Implementation

This paper presents the implementation and computational validation of a compatibility-based strut-and-tie model (C-STM) presented in a companion paper intended for analyzing the nonlinear force-deformation behavior of disturbed regions and structural concrete deep beams. The C-STM is used to predict the force-deformation response and internal nonlinear strain behavior of previously conducted large-scale reinforced concrete bridge bent-cap experiments. Additionally, the experimental results are compared with current code-based approaches to illustrate how the C-STM can be used as a minimalist computational analysis tool to provide an accurate prediction of the structures force-displacement response. A comprehensive description of how the C-STM is implemented into structural analysis software SAP2000TM is given to provide a step-by-step modeling procedure that can be replicated by practicing engineers seeking to apply this modeling procedure to other facets of research and design.

Modified Yield Line Theory for Full-Depth Precast Concrete Bridge Deck Overhang Panels

Full-depth precast deck slab cantilevers also referred to as full-depth precast concrete bridge deck overhang panels are becoming increasingly popular in concrete bridge deck construction. To date, no simple theory is able to estimate the overhang capacity of full-depth concrete bridge deck slabs accurately. Observations suggest that interaction between flexure and shear is likely to occur as neither alone provides an accurate estimate of the load-carrying capacity. Therefore, modified yield line theory is presented in this paper, which accounts for the development length of the mild steel reinforcing to reach yield strength. Failure of the full-depth panels is influenced by the presence of the partial-depth transverse panel-to-panel seam. When applying a load on the edge of the seam, the loaded panel fails under flexure while the seam fails in shear. Through the use of the modified yield line theory coupled with a panel-to-panel shear interaction, analytical predictions are accurate within 1–6% of experimental results for critical cases.