Preliminary analytical study on seismic ductility demand of wood diaphragms

A new seismic design methodology is being proposed for floor diaphragms for various types of construction materials including wood diaphragms. The new design methodology introduces a design acceleration to keep diaphragm elastic under design-basis earthquake using a mode superposition method. On top of this elastic design acceleration, a force reduction factor is proposed in the design methodology by considering available diaphragm ductility capacity and possible post-yielding strain hardening

Development of diaphragm connector elements for three-dimensional nonlinear dynamic analysis of precast concrete structures

Diaphragm connector elements were developed for three-dimensional finite element models of precast concrete structures used in nonlinear time history analyses. The use of discrete elements for the diaphragm connectors permits the direct evaluation of local force and deformation demands, information needed in calibrating design factors for a new diaphragm seismic design methodology. This article describes the element formulation. The connector elements consist of assemblages of standard elements readily available in most finite element software libraries. The connector element calibration is based on full-scale testing of common precast diaphragm connectors. In these tests, the connector exhibited hysteretic pinching, stiffness/strength degradation, and slip mechanisms. The diaphragm connector elements were constructed to capture these behaviors to an accuracy sufficient for establishing viable design factors, while still appropriate for insertion into large degree-of-freedom models. The models are validated against the results of simulation-driven tests for critical precast diaphragm joints and a half-scale shake table test

Sudden Event Monitoring of Civil Infrastructure Using Demand-Based Wireless Smart Sensors

Wireless smart sensors (WSS) have been proposed as an effective means to reduce the high cost of wired structural health monitoring systems. However, many damage scenarios for civil infrastructure involve sudden events, such as strong earthquakes, which can result in damage or even failure in a matter of seconds. Wireless monitoring systems typically employ duty cycling to reduce power consumption; hence, they will miss such events if they are in power-saving sleep mode when the events occur. This paper develops a demand-based WSS to meet the requirements of sudden event monitoring with minimal power budget and low response latency, without sacrificing high-fidelity measurements or risking a loss of critical information. In the proposed WSS, a programmable event-based switch is implemented utilizing a low-power trigger accelerometer; the switch is integrated in a high-fidelity sensor platform. Particularly, the approach can rapidly turn on the WSS upon the occurrence of a sudden event and seamlessly transition from low-power acceleration measurement to high-fidelity data acquisition. The capabilities of the proposed WSS are validated through laboratory and field experiments. The results show that the proposed approach is able to capture the occurrence of sudden events and provide high-fidelity data for structural condition assessment in an efficient manner

Development of deformable connection for earthquake-resistant buildings to reduce floor accelerations and force responses

This paper presents the development of a deformable connection that is used to connect each floor system of the flexible gravity load resisting system (GLRS) with the stiff lateral force resisting system (LFRS) of an earthquake-resistant building. It is shown that the deformable connection acts as a seismic response modification device, which limits the lateral forces transferred from each floor to the LFRS and allows relative motion between the GLRS and LFRS

Optimization of Mixture Parameter for Physical and Mechanical Properties of Reactive Powder Concrete under External Sulfate Attack using Taguchi Method

Reactive powder concrete (RPC) is defined as a cementitious composite material with an optimized size of granular constituents, very low water-to-binder ratio (w/b), pozzolanic materials like silica fume (SF), and discontinuous fiber reinforcement. RPC applications include bridge decks and girders, seismic columns, wind turbine towers, and pile foundations. Especially, a durable and robust RPC pile foundation with long service life is essential in building construction because continuous maintenance is impossible. Moreover, natural in-situ conditions such as water table, temperature, and sulfate concentration in soil to which the pile foundation is exposed are critical and related to deteriorating the pile foundation. Therefore, the Taguchi design of experiments (DOE) was used in this research to determine the optimal RPC mixture with beneficial characteristics against external sulfate attack (ESA). Mixture design parameters included steel fiber content (0, 1 and 2 %), w/b (0.16, 20 and 0.24), and SF content (15, 20 and 25 %). In contrast, environmental conditions of ESA exposure contained three different sodium sulfate (Na2SO4) concentrations (0.35, 1.05, and 3.15 M), cyclic and continuous exposure at normal temperature (20 °C), and continuous exposure at elevated temperatures (40 °C and 60 °C). The analytical and statistical investigation evaluated mass change, compressive strength, and modulus of rupture in RPC mixtures exposed to these conditions for 52 weeks. Test results show that cyclic exposure and increased solution temperature in ESA facilitate RPC damage. If measured after air drying, RPC mixtures subjected to cyclic ESA are especially susceptible to failure. Taguchi analysis indicated the optimum parameters\u27 level for mass change as: 0 % steel fiber, w/b = 0.16, and 20 % SF content; for the compressive strength: 2 % steel fiber, w/b = 0.24, and 20 % SF content; and, for modulus of rupture: 2 % steel fiber, w/b = 0.20, and 25 % SF content. In conclusion, RPC appears to be sustainable and durable material under different ESA exposure conditions

Evaluating feasibility of modified drilling waste materials in flexible base course construction

The study focuses on the evaluation of the engineering properties of modified drilling waste materials (MDWMs) as base course materials in roadway construction. This goal was accomplished by two main laboratory test evaluations of the MDWMs which are the basic material characterization and the performance evaluation of base course material

Statistical Analysis of Sulfate Attack Resistance of Reactive Powder Concrete

This paper is the study of sulfate attack resistance of reactive powder concrete (RPC). RPC that is also known as ultra-high performance concrete is a special type of concrete material obtained when fine powders like silica fume (SF) are added into the concrete mortar along with very low waterto-binder ratio (w/b). SF is a pozzolanic material obtained as a by-product of silicon metal or ferrosilicon alloys production. In this study, total 6 different RPC mixtures with various w/b (0.18, 0.22 and 0.26) and various SF content were studied. SF was added into the concrete mixtures in the amount of 15%, 20% and 25% of cement by weight. The other testing parameter includes 3 different concentrations of sodium sulfate (Na2SO4) solutions (0.35 M, 0.7 M and 1.4 M concentrations). Broad laboratory investigations of behavior of the RPC mixtures were conducted in terms of compressive strength and mass gain of cubes (50×50×50 mm3) and expansion and mass change as in accordance with ASTM C1012. Test results had been analyzed and assessed by Taguchi method. The significance level of experimental parameters was determined by using Analysis of variance (ANOVA) method. According to statistical and analytical results it was observed that RPC has high sulfate attack resistance. Moreover, addition of optimal amount of SF into the RPC mixtures as well as decreasing w/b can significantly improve Na2SO4 resistance of RPC

Photocatalytic cementitious material for eco-efficient construction—a systematic literature review

Photoinduced processes governed by light activated TiO2 have been studied in many ways. One of the most active areas is the development of TiO2 photocatalysis technologies on their application for reducing environmental impacts. The immobilization of TiO2 on solid support, such as cementitious materials, greatly enhances its use in practical applications. In this review, a wide range of applications for achieving eco-efficient building using cementitious composite materials containing TiO2 photocatalyst was presented. The basic mechanism of photocatalysis, such as electron excitation, charge transfer process, reactive oxygen species (ROS) generation, and its role to oxidize the pollutant and microorganisms were extensively discussed. Unlike self-cleaning and air purification systems, the study on the antibacterial function of a cement-based surface containing TiO2 is very limited. In photocatalytic cementitious materials, the key element affecting the photocatalytic performance is the accessible active surface area. However, microstructure of cementitious materials changes with age due to hydration and surface carbonation. Hence, surface area reduction and mass transfer limitation become the main drawbacks of incorporating TiO2 in cementitious materials. This review, therefore, provides the state of the art in photocatalytic cement-based composite materials and identifies the areas in which future improvement is needed

MECHANICAL, SWELLING, AND THERMAL PROPERTIES OF GEOPOLYMER MIXTURE CONTAINING BASIC OXYGEN FURNACE SLAG AGGREGATES

Basic oxygen furnace slag (BOFS) is a waste product generated during steel production. The utilization of BOFS in construction applications is considerably limited because of its inherent characteristics leading to volumetric expansion behavior caused by the chemical reaction between free lime (f-CaO) and water. The main objective of this paper is to investigate the material properties of normal mortar and geopolymer mixtures that contain BOFS aggregates. Three different aggregates were used to compare their performance, including siliceous river sand, fresh BOFS aggregate (within 1-month age), and stockpiled (more than 5-year age) BOFS aggregate. Test methods included a compressive strength test, accelerated mortar bar expansion test, and thermal conductivity test. Test results revealed that (1) geopolymer mixtures containing BOFS aggregate had comparable compressive strength with mortar mixture with river sand, (2) geopolymer mixtures have very low volume expansion, (3) thermal conductivity of geopolymer mixtures having both river sand and BOFS was lower than normal cement mortar mixture containing river sand. Therefore, geopolymer technology seems a key solution for converting BOFS slag into valuable construction materials. Therefore, a geopolymer mixture containing BOFS aggregate can be used as an energy-saving material

EXAMINATION OF PRECAST CONCRETE DIAPHRAGM SEISMIC RESPONSE BY THREE-DIMENSIONAL NONLINEAR TRANSIENT DYNAMIC ANALYSES

The primary objective of the dissertation research is to establish the seismic demands of precast concrete floor diaphragms designed with an emerging design methodology. To accomplish this, three-dimensional (3D) finite element (FE) models of diaphragm-sensitive precast concrete structures have been developed by extending two-dimensional (2D) diaphragm model developed previously for nonlinear static "pushover" analyses. Using these models, diaphragm seismic demands under expected hazard are evaluated through the nonlinear transient dynamic analyses (NLTDA).The research work is composed of four major parts:(1) Developing 3D NLTDA analytical model for diaphragm-sensitive precast concrete structures: The 3D structure model is extended from a 2D FE diaphragm model developed by a previous researcher. This process involves properly handling comparability conditions in 3D, incorporating proper hysteresis behavior for the diaphragm reinforcement, and developing appropriate lateral force resisting system (LFRS) models. A sensitivity analysis is performed for 3D NLTDA modeling to assist in creating an appropriate model.(2) Application of the model in integrated analysis-driven physical testing: These experiments occurred at Lehigh University (LU) with project collaborators. The loading in these tests were controlled by NLTDA of the 3D analytical model. The tests were used to examine the seismic response of key joints (critical flexure and shear joints) in the diaphragm under realistic demands and to further calibrate the analytical model.(3) Analytical modeling in support of shake table testing: The shake table test was performed at University of California San Diego (UCSD). The test involved a half scale three-story diaphragm-sensitive precast concrete structure. NLTDA using the 3D analytical model is used to assist in design and performance prediction of the test specimen. The test results are being used to calibrate/verify the analytical model.(4) Calibrating design factors for the emerging diaphragm design methodology: In the last research step, the 3D analytical model is used to calibrate trial design factors for the emerging diaphragm design methodology. These factors are established based on a parametric study of NLDTA at different seismic hazard levels using simple structure configurations. These factors will be evaluated on models of realistic structures to determine design factors for the final design procedure