Seismic vulnerability of buildings and non-structural elements: insights from the 2011 Lorca earthquake

This PhD dissertation presents a profound study of the vulnerability of buildings and non-structural elements stemming from the investigation of the Mw 5.2 Lorca 2011 earthquake; which constitutes one of the most significant earthquakes in Spain. It left nine fatalities due to falling debris from reinforced concrete buildings, 394 injured and material damage valued at 800 million euros. Within this framework, the most relevant initiatives concerning the vulnerability of buildings and the exposure of Lorca are studied. This work revealed two lines of research: the elaboration of a rational method to determine the adequacy of a specific fragility curve for the particular seismic risk study of a region; and the relevance of researching the seismic performance of non-structural elements. As a consequence, firstly, a method to assess and select fragility curves for seismic risk studies from the catalogue of those available in the literature is elaborated and calibrated by means of a case study. The said methodology is based on a multidimensional index and provides a ranking that classifies the curves in terms of adequacy. Its results for the case of Lorca led to the elaboration of new fragility curves for unreinforced masonry buildings. Moreover, a simplified method to account for the unpredictable directionality of the seism in the creation of fragility curves is contributed. Secondly, the characterisation of the seismic capacity and demand of the non-structural elements that caused most of the human losses is studied. Concerning the capacity, an analytical approach derived from theoretical considerations to characterise the complete out-of-plane seismic response curve of unreinforced masonry cantilever walls is provided; as well as a simplified and more practical trilinear version of it. Concerning the demand, several methods for characterising the Floor Response Spectra of reinforced concrete buildings are tested through case studies.

Vibratory Effects in Reinforced Portland Cement Concrete Pavement, MLR-97-2, 1997

A double mat of reinforcement steel consisting of No. 5 bars was placed in the longitudinal and transverse directions in a 26' wide, 10" thick pavement. The bars were placed on 12" centers with 2" of cover from the top and bottom surfaces. The special reinforcement is to provide additional strength in the pavement over an area of old coal mine tunnels. Auxiliary and standard paver vibrators were used to consolidate the concrete. There was concern that over-vibration could be occurring in some areas and also that a lack of consolidation may be occurring under the steel bars in some areas. A core evaluation study of the pavement was developed. The results showed that the consolidation and the air contents were satisfactory. Additional paving with reinforcement in the same area should use the same or similar method and amount of vibration as was used in the area evaluated in this study.

Bonded, Thin-Lift, Non-Reinforced Portland Cement Concrete Resurfacing, HR-191, 1980

A Research Project involving two, three, four and five inches of bonded Portland Cement Concrete Overlay on a 1.3 mile Portland Cement Concrete pavement was conducted in Clayton County, Iowa, during September, 1977, centering on the following objectives: 1. Determine the mixing and proportioning procedures required in using a conventional, central mix proportioning plant to produce a dense Portland Cement Concrete mixture using standard mixes with super-water reducing admixtures; 2. Determine the economics, longevity and maintenance performance of a bonded, thin-lift, non-reinforced Portland Cement Concrete resurfacing course using conventional procedures, equipment and concrete paving mixtures both with and without super-water reducing admixtures; 3. Determine if an adequate bond between the existing pavement and an overlay of thin-lift, dense, non-reinforced Portland Cement Concrete can be obtained with only special surface cleaning and no surface removal or grinding.

Deterioration of Iowa Highway Concrete Pavements: A Petrographic Study, HR-1065, 1999

Major highway concrete pavements in Iowa have exhibited premature deterioration attributed to effects of ettringite formation, alkali-silica expansive reactions, and to frost attack, or some combination of them. These pavements were constructed in the mid- 1980s as non-reinforced, dual-lane, roads ranging in thickness between 200 mm and 300 mm, with skewed joints reinforced with dowels. Deterioration was initially recognized with a darkening of joint regions, which occurred for some pavements as soon as four years after construction. Pavement condition ranges from severe damage to none, and there appeared to be no unequivocal materials or processing variables correlated with failure. Based upon visual examinations, petrographic evaluation, and application of materials models, the deterioration of concrete highway pavements in Iowa appear related to a freeze-thaw failure of the coarse aggregate and the mortar. Crack patterns sub-parallel to the concrete surface transecting the mortar fraction and the coarse aggregate are indicative of freeze-thaw damage of both the mortar and aggregate. The entrained air void system was marginal to substandard, and filling of some of the finer-sized voids by ettringite appears to have further degraded the air void system. The formation of secondary ettringite within the entrained air voids probably reflects a relatively high degree of concrete saturation causing the smaller voids to be filled with pore solution when the concrete freezes. Alkali-silica reaction (ASR) affects some quartz and shale in the fine aggregate, but is not considered to be a significant cause of the deterioration. Delayed ettringite formation was not deemed likely as no evidence of a uniform paste expansion was observed. The lack of field-observed expansion is also evidence against the ASR and DEF modes of deterioration. The utilization of fly ash does not appear to have affected the deterioration as all pavements with or without fly ash exhibiting substantial damage also exhibit significant filling of the entrained air void system, and specimens containing fly ash from sound pavements do not have significant filling. The influence of the mixture design, mixing, and placing must be evaluated with respect to development of an adequate entrained air void system, concrete homogeneity, longterm drying shrinkage, and microcracking. A high-sand mix may have contributed to the difficult mixture characteristics noted upon placement and exacerbate concrete heterogeneity problems, difficulty in developing an adequate entrained air void system, poor consolidation potential, and increased drying shrinkage and cracking. Finally, the availability of moisture must also be considered, as the secondary precipitation of ettringite in entrained air voids indicates they were at least partially filled with pore solution at times. Water availability at the base of the slabs, in joints, and cracks may have provided a means for absorbing water to a point of critical saturation.

New recycling approaches for thermoset polymeric composite wastes – an experimental study on polyester based concrete materials filled with fibre reinforced plastic recyclates

In this study, a new waste management solution for thermoset glass fibre reinforced polymer (GFRP) based products was assessed. Mechanical recycling approach, with reduction of GFRP waste to powdered and fibrous materials was applied, and the prospective added-value of obtained recyclates was experimentally investigated as raw material for polyester based mortars. Different GFRP waste admixed mortar formulations were analyzed varying the content, between 4% up to 12% in weight, of GFRP powder and fibre mix waste. The effect of incorporation of a silane coupling agent was also assessed. Design of experiments and data treatment was accomplished through implementation of full factorial design and analysis of variance ANOVA. Added value of potential recycling solution was assessed by means of flexural and compressive loading capacity of GFRP waste admixed mortars with regard to unmodified polymer mortars. The key findings of this study showed a viable technological option for improving the quality of polyester based mortars and highlight a potential cost-effective waste management solution for thermoset composite materials in the production of sustainable concrete-polymer based products.

PLSR Models for Mechanical Strengths of Concrete Composite Materials Reinforced with Pultrusion Wastes

In this paper, we present two Partial Least Squares Regression (PLSR) models for compressive and flexural strength responses of a concrete composite material reinforced with pultrusion wastes. The main objective is to characterize this cost-effective waste management solution for glass fiber reinforced polymer (GFRP) pultrusion wastes and end-of-life products that will lead, thereby, to a more sustainable composite materials industry. The experiments took into account formulations with the incorporation of three different weight contents of GFRP waste materials into polyester based mortars, as sand aggregate and filler replacements, two waste particle size grades and the incorporation of silane adhesion promoter into the polyester resin matrix in order to improve binder aggregates interfaces. The regression models were achieved for these data and two latent variables were identified as suitable, with a 95% confidence level. This technological option, for improving the quality of GFRP filled polymer mortars, is viable thus opening a door to selective recycling of GFRP waste and its use in the production of concrete-polymer based products. However, further and complementary studies will be necessary to confirm the technical and economic viability of the process.

Durability aspects related to rubble stone masonry walls strengthened with reinforced micro-concrete layers

International Seminar on Seismic Risk and Rehabilitation of Stone Masonry Housing, Azores, Portugal, 1998

The influence of fibre orientation on the post-cracking tensile behaviour of steel fibre reinforced self-compacting concrete

Adding fibres to concrete provides several advantages, especially in terms of controlling the crack opening width and propagation after the cracking onset. However, distribution and orientation of the fibres toward the active crack plane are significantly important in order to maximize its benefits. Therefore, in this study, the effect of the fibre distribution and orientation on the post-cracking tensile behaviour of the steel fibre reinforced self-compacting concrete (SFRSCC) specimens is investigated. For this purpose, several cores were extracted from distinct locations of a panel and were subjected to indirect (splitting) and direct tensile tests. The local stress-crack opening relationship (σ-w) was obtained by modelling the splitting tensile test under the finite element framework and by performing an Inverse Analysis (IA) procedure. Afterwards the σ-w law obtained from IA is then compared with the one ascertained directly from the uniaxial tensile tests. Finally, the fibre distribution/orientation parameters were determined adopting an image analysis technique.

Tensile stress–crack width law for steel fibre reinforced self-compacting concrete obtained from indirect (splitting) tensile tests

In this work, the fracture mode I parameters of steel fibre reinforced self-compacting concrete (SFRSCC) were derived from the numerical simulation of indirect splitting tensile tests. The combined experimental and numerical research allowed a comparison between the stress-crack width (σ - w) relationship acquired straightforwardly from direct tensile tests, and the σ - w response derived from inverse analysis of the splitting tensile tests results. For this purpose a comprehensive nonlinear 3D finite element (FE) modeling strategy was developed. A comparison between the experimental results obtained from splitting tensile tests and the corresponding FE simulations confirmed the good accuracy of the proposed strategy to derive the σ – w for these composites. It is concluded that the post-cracking tensile laws obtained from inverse analysis provided a close relationship with the ones obtained from the experimental uniaxial tensile tests.

Assessment of the performance of steel fibre reinforced self-compacting concrete in elevated slabs

The reinforcement mechanisms at the cross section level assured by fibres bridging the cracks in steel fibre reinforced self-compacting concrete (SFRSCC) can be significantly amplified at structural level when the SFRSCC is applied in structures with high support redundancy, such is the case of elevated slab systems. To evaluate the potentialities of SFRSCC as the fundamental material of elevated slab systems, a ¼ scale SFRSCC prototype of a residential building was designed, built and tested. The extensive experimental program includes material tests for characterizing the relevant properties of SFRSCC, as well as structural tests for assessing the performance of the prototype at serviceability and ultimate limit conditions. Three distinct approaches where adopted to derive the constitutive laws of the SFRSCC in tension that were used in finite element material nonlinear analysis to evaluate the reliability of these approaches in the prediction of the load carrying capacity of the prototype.

Time-dependent flexural behaviour of cracked steel fibre reinforced self-compacting concrete panels

In the present work are described and discussed the results of an extensive experimental program that aims to study the long-term behaviour of cracked steel fibre reinforced self-compacting concrete, SFRSCC, applied in laminar structures. In a first stage, the influence of the initial crack opening level (wcr = 0.3 and 0.5 mm), applied stress level, fibre orientation/dispersion and distance from the casting point, on the flexural creep behaviour of SFRSCC was investigated. Moreover, in order to evaluate the effects of the creep phenomenon on the residual flexural strength, a series of monotonic tests were also executed. It was found that wcr = 0.5 mm series showed a higher creep coefficient comparing to the series with a lower initial crack opening. Furthermore, the creep performance of the SFRSCC was influenced by the orientation of the extracted prismatic specimens regarding the direction of the concrete flow within the cast panel.

Evaluation of the performance of steel fibre reinforced self-compacting concrete in elevated slab systems; from the material to the structure

Degree of Doctor of Philosophy of Structural/Civil Engineering

Field Evaluation of Elliptical Fiber Reinforced Polymer Dowel Performance, June 2005

Fiber reinforced polymer (FRP) composite materials are making an entry into the construction market in both buildings and pavements. The application to pavements so far has come in the form of joint reinforcement (dowels and tie bars). FRP resistance to salt corrosion in dowels has made it an alternative to standard epoxy-coated steel dowels for pavements. Iowa State University has completed a large amount of laboratory research to determine the diameter, spacing, and durability of FRP dowels. This report documents the performance of elliptical FRP dowels installed in a field situation. Ten joints were monitored in three consecutive test sections, for each of three dowel spacings (10, 12, and 15 inches) including one instrumented dowel in each test section. The modulus of dowel bar support was determined using falling weight deflectometer (FWD) testing and a loaded crawl truck. FWD testing was also used to determine load transfer efficiency across the joint. The long-term performance and durability of the concrete was also evaluated by monitoring faulting and joint opening measurements and performing visual distress surveys at each joint. This report also contains similar information for standard round, medium elliptical, and heavy elliptical steel dowels in a portion of the same highway. In addition, this report provides a summary of theoretical analysis used to evaluate joint differential deflection for the dowels.

Evaluating Properties of Blended Cements for Concrete Pavements, December 2003

The addition of supplementary cementitious materials (SCMs), such as fly ash (FA) and slag, generally improves concrete workability, durability, and long-term strength. New trends in sustainable development of concrete infrastructure and in environmental regulations on waste disposal are spurring use of SCMs in concrete. However, use of SCM concrete is sometimes limited due to a lack of understanding about material behaviors and lack of proper specifications for its construction practice. It is believed that SCM concrete performance varies significantly with the source and proportion of the cementitious materials. SCM concrete often displays slower hydration, accompanied by slower setting and lower early-age strength, especially under cold weather conditions. The present research was conducted to have a better understanding of SCM concrete behaviors under different weather conditions. In addition to the study of the effect of SCM content on concrete set time using cementitious materials from different sources/manufacturers, further research may be needed to investigate the effects of SCM combinations on concrete flowability, air stability, cracking resistance, and durability.

Development of In-Situ Detection Methods for Materials-Related Distress (MRD) in Concrete Pavements, July 2003

The purpose of this research was to summarize existing nondestructive test methods that have the potential to be used to detect materials-related distress (MRD) in concrete pavements. The various nondestructive test methods were then subjected to selection criteria that helped to reduce the size of the list so that specific techniques could be investigated in more detail. The main test methods that were determined to be applicable to this study included two stress-wave propagation techniques (impact-echo and spectral analysis of surface waves techniques), infrared thermography, ground penetrating radar (GPR), and visual inspection. The GPR technique was selected for a preliminary round of “proof of concept” trials. GPR surveys were carried out over a variety of portland cement concrete pavements for this study using two different systems. One of the systems was a state-of-the-art GPR system that allowed data to be collected at highway speeds. The other system was a less sophisticated system that was commercially available. Surveys conducted with both sets of equipment have produced test results capable of identifying subsurface distress in two of the three sites that exhibited internal cracking due to MRD. Both systems failed to detect distress in a single pavement that exhibited extensive cracking. Both systems correctly indicated that the control pavement exhibited negligible evidence of distress. The initial positive results presented here indicate that a more thorough study (incorporating refinements to the system, data collection, and analysis) is needed. Improvements in the results will be dependent upon defining the optimum number and arrangement of GPR antennas to detect the most common problems in Iowa pavements. In addition, refining highfrequency antenna response characteristics will be a crucial step toward providing an optimum GPR system for detecting materialsrelated distress.