Abstract

Structural and forensic analysis concluded that the Arecibo Observatory M4N socket joint failure in August 2020 was due to a socket joint design with insufficient design criteria that did not explicitly consider socket constituent stress margins or time-dependent damage mechanisms. The socket attachment design was found to have an initially low structural margin with a finite service life, notably in the outer socket wires, which degraded primarily due to long-term zinc creep effects that were activated by longterm sustained loading and exacerbated by cyclic loading. Additionally, HAC and wire defects were found in a few outer wires that may also have contributed to initial outer wire failures. The design did not explicitly consider the time-dependent effects of creep and cyclic loading on design capability, account for a worstcase build condition traceable to in-service inspection of features (e.g., zinc creep/extrusion), specify an end-of-life capability requirement associated with service life degradation, or explicitly set service life inspection intervals with pass/fail inspection criteria. In-service inspections showed evidence of progressive zinc extrusion on several Arecibo sockets, which in hindsight were evidence of cumulative damage and effectively a missed opportunity to prevent cable failure. Open spelter sockets of this type are used throughout industry in stay cables. The following recommendations are proposed to prevent failures of similar socket joints: (1) Verification of positive stress margins in socket joint wires for all failure modes, (2) Periodic visual inspections with acceptance criteria for zinc extrusion that are tied to structural qualification, (3) Revisiting civil codes and industry standards based on lessons learned from this analysis. 

Abstract

A quantitative risk analysis is presented for a gas pipeline system in the province of Córdoba, Argentina. This is a part of a project on the vulnerability of infrastructure and physical environment associated with the storage and transport of combustible fluids. The developed model considers the identification of threats to the integrity of the pipelines, an estimate of the probabilities of failure of the identified threats, an estimate of the consequences of a failure, the determination and evaluation of the quantitative risk according to acceptance criteria, and the adoption of risk mitigation and control measures. For this study, the main data from the existing backbone network and the recently built gas pipelines in the province of Córdoba are used. This is complemented with a survey of the constructions near the route of the sections under study, as well as the crossings of roads and watercourses, based on available satellite images. The work is focused on establishing the individual and social quantitative risk levels of the gas pipelines with the highest qualitative risk level, already defined by previous work. Finally, and in the necessary cases, the adoption of mitigation measures is considered to adjust the risk levels to the international acceptance criteria.  A quantitative risk analysis is presented for a gas pipeline system in the province of Córdoba, Argentina. This is a part of a project on the vulnerability of infrastructure and physical environment associated with the storage and transport of combustible fluids. The developed model considers the identification of threats to the integrity of the pipelines, an estimate of the probabilities of failure of the identified threats, an estimate of the consequences of a failure, the determination and evaluation of the quantitative risk according to acceptance criteria, and the adoption of risk mitigation and control measures. For this study, the main data from the existing backbone network and the recently built gas pipelines in the province of Córdoba are used. This is complemented with a survey of the constructions near the route of the sections under study, as well as the crossings of roads and watercourses, based on available satellite images. The work is focused on establishing the individual and social quantitative risk levels of the gas pipelines with the highest qualitative risk level, already defined by previous work. Finally, and in the necessary cases, the adoption of mitigation measures is considered to adjust the risk levels to the international acceptance criteria. 

Abstract

The most recent update of the Seismic Hazard Map of Puerto Rico was carried out in 2003 when the first active seismic fault within the island, in the Cabo Rojo area, was considered. Since then, several geophysical studies have been carried out on various seismic faults within the island that have helped to expand the knowledge of these faults and, in some cases, to recognize their high seismic activity. The Seismic Sequence that began in December 2019 produced more than thirteen thousand earthquakes in 2020, with a large percentage of them having their epicenter within the Island. The overwhelming evidence of active seismic faults within the Island urges the prompt update of the Seismic Hazard Map. However, multiple studies are needed to determine with accepted precision the location, size and slip rate of these faults so that they can be included in the Seismic Hazard Map. In the meantime, engineers urgently require a proper estimate of the seismic loads that these faults, not thoroughly studied, can apply to the structures to be designed or rehabilitated. In this paper we use the current knowledge of the existing earthquake fault zones and the deterministic methodology of ASCE 7-16 to develop design spectra for twelve municipalities of Puerto Rico taking into consideration all the earthquake fault zones that constantly threaten the Island. In average, the proposed spectra almost double the design seismic loads required by the current 2018 IBC code. 

Abstract

The Synthetic Lightweight Aggregates (SLA) is a patented aggregate composed of fly ash and high-density polyethylene (HDPE). It is considered as an eco-friendly material because its use would contribute to reduce the amount of waste going to landfills. One of most promising applications of SLA is related with the geotechnical engineering field because of its low density that when combined with natural soils may produce a composite backfill material with adequate mechanical properties. This research focuses on testing SLA material properties, including material characterization, trial mixes of SLA with natural aggregates, and compaction tests to obtain the optimum dry density. The composite soil meets the AASHTO classification standards for A-2-4 soils. The validation of the observed behavior lead to propose at least three basic applications related with natural disasters prevention: a) efficient design of retaining walls with lower lateral pressures, b) control of settlements using low density composite soils over compressible soils, and c) slope stability problems.

Abstract

Hurricane María was an extreme atmospheric event that impacted Puerto Rico in 2017. As a result of the passage of hurricane María over the island more than 70,000 landslides were triggered, with the highest density of mass wasting found in the mountainous center of the island. This area is highly susceptible to slope failure given the local soils that form as a result of continuous tropical chemical weathering of the bedrock material. Copious amounts of sediment from these soils were mobilized and transported by the landslide-triggering event. The results of our study reveal the soil types that are most susceptible to mass wasting loss in order to better understand their susceptibility to failure and contribution to sedimentation across the rugged interior of the island. A preliminary analysis of area volume scaling statistics for thousands of landslide sites in the important Lago Dos Bocas basin reveals that Hurricane María likely liberated at least 1.7 million cubic meters of mostly superficial sediment in the lake’s contributing area (not including the Caonillas sub-basin). In an effort to determine the efficiency of the fluvial system to transport these sediments during and after the catastrophic hurricane event, bathymetric surveying was carried out in Lago Dos Bocas, where much of the sediment is hypothesized to have been deposited. This reservoir is a vital piece of infrastructure in the island as it supplies water to the San Juan metropolitan area. Based on the 2021 bathymetric survey and the historical data, the excess sediment deposition to the reservoir related to Hurricane María is estimated at approximately 2.1 million cubic meters. When compared with data from 1999-2010, this volume represents the equivalent of 18 years of background sedimentation. At present, the reservoir capacity loss since construction is at 64%. These analyses are pertinent to understand how the local sediment budget has been affected and to re-calculate the useful life of the reservoir and highlight the vulnerability of Caribbean infrastructure systems, given the forecasted likelihood of increased tropical cyclone activity in the years to come. 

Abstract

Synthetic strong motion records for the 1991, Mw 7.6, Limón, Cosa Rica earthquake were computed for several hundred different source models. The rotd50 (response spectra) was used to compare synthetic and observed data at seven stations that recorded the event. The source model that minimized the misfit was selected to calculate new synthetic records at present-day stations. The result indicated that the fault length reached some 100 km long by 40 km deep. The largest peak ground acceleration would have been recorded in the stations located along the Caribbean coast, close to the epicenter. A post-earthquake bridge inspection calculation using our scenario earthquake predicted a high level of damage to several bridges that collapsed in 1991.