A Proposal to Improve the Effectiveness of the Deflection Control Method Provided by Eurocodes for Concrete, Timber, and Composite Slabs

Limited deflection of structural members represents an important requirement to guarantee proper functionality and appearance of building and infrastructures. According to Eurocodes, this requirement is ensured by limiting the maximum deflection of horizontal structural members to a fraction of their span. However, each Eurocode provides different maximum deflection limits, which are independent of the type of superstructures considered. Thus, the respect of these limits may not always guarantee the integrity of certain superstructures. In this paper, the reliability of the Eurocode deflection control methods, in guaranteeing the integrity of the superstructures, is assessed and discussed. First, different types of horizontal member, namely rib and clay (hollow) pot, composite steel–concrete, and timber beam slabs are designed to respect the deflection limit enforced by the Eurocodes. Then, the maximum curvature developed by these members is compared with the ultimate (limit) curvatures of various superstructures (e.g., ceramic and stone tile floorings). The results obtained show that the approach adopted by Eurocode 2 may provide non-conservative results, but also that the rules proposed by Eurocodes 4 and 5, albeit more reliable, do not always guarantee the integrity of the superstructure. Based on these results, an alternative method, based on the curvature control, is proposed and its advantages and limitations critically discussed. This method appears simpler and more reliable than the method currently adopted by the Eurocodes.

Current and New Approaches to Predict the Deflections of One-Way Flexural Members with a Focus on Composite Steel Deck Slabs Voided by Circular Tubes

A new type of composite voided slab, the TUBEDECK (TD), which utilizes the structural function of profiled steel decks, has recently been proposed. Previous studies have confirmed that the flexural strength of TD slabs can be calculated based on the full composite contribution of the steel deck, but for long-span flexural members, the deflection serviceability requirement is often dominant. Herein, we derived a novel deflection prediction approach using the results of flexural tests on slab specimens, focusing on TD slabs. First, deflection prediction based on modifications of the current code was proposed. Results revealed that TD slabs exhibited smaller long-term deflections and at least 10% longer maximum span lengths than solid slabs, indicating their greater efficiency. Second, a novel rational method was derived for predicting deflections without computing the effective moment of inertia. The ultimate deflections predicted by the proposed method correlated closely with the deflection under maximum bending moments. To calculate immediate deflections, variation functions for the concrete strain at the extreme compression fiber and neutral axis depth were assumed with predictions in good agreement with experiments. The proposed procedure has important implications in highlighting a new perspective on the deflection prediction of reinforced concrete and composite flexural members.

Distributed Fiber Optic Measurements of Strain and Temperature in Long-Span Composite Floor Beams with Simple Shear Connections Subject to Compartment Fires

This study explores an instrumentation strategy using distributed fiber optic sensors to measure strain and temperature through the concrete volume in large-scale structures. Single-mode optical fibers were deployed in three 12.8 m long steel and concrete composite floor specimens tested under mechanical or combined mechanical and fire loading. The concrete slab in each specimen was instrumented with five strain and temperature fiber optic sensors along the centerline of the slab to determine the variation of the measurands through the depth of the concrete. Two additional fiber optic temperature sensors were arranged in a zigzag pattern at mid-depth in the concrete to map the horizontal spatial temperature distribution across each slab. Pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA) was used to determine strains and temperatures at thousands of locations at time intervals of a few minutes. Comparisons with co-located strain gauges and theoretical calculations indicate good agreement in overall spatial distribution along the length of the beam tested at ambient temperature, while the fiber optic sensors additionally capture strain fluctuations associated with local geometric variations in the specimen. Strain measurements with the distributed fiber optic sensors at elevated temperatures were unsuccessful. Comparisons with co-located thermocouples show that while the increased spatial resolution provides new insights about temperature phenomena, challenges for local temperature measurements were encountered during this first attempt at application to large-scale specimens.

II: Thermal-structural analysis

This paper describes a reduced-order modeling approach for thermal and structural analysis of fire effects on composite slabs with profiled steel decking. The reduced-order modeling approach, which uses alternating strips of layered shell elements to represent the thick and thin portions of the slab, allows both thermal and structural analyses to be performed using a single model. The modeling approach accounts for the trapezoidal profile of the concrete in the ribs; the structural resistance provided by the steel decking, including the webs of the decking; and the orthotropic behavior of the decking, which provides greater resistance along the ribs than transverse to the ribs. The modeling approach is validated against experimental data from one-way composite slabs tested under ambient-temperature, a one-way composite slab tested under fire conditions, and a two-way composite slab tested under fire conditions. Both implicit and explicit solution schemes are evaluated for the structural analysis, and the results show that it is feasible to scale down the hours-long fire duration to a simulation time of seconds in an explicit dynamic analysis, without adversely affecting the accuracy of the results. The steel decking contributes significantly to the structural resistance at ambient temperature, but as expected, its contribution is found to decrease rapidly under fire exposure. The modeling approach can account for the location of reinforcing bars (i.e., at a specified depth in either the thick or thin portion of the slab), and it is found that reinforcement location can have a significant effect on the structural response, because heat transfer in the composite slab results in higher temperatures in the thin portions of the slab between the ribs.

Application of PZT Technology and Clustering Algorithm for Debonding Detection of Steel-UHPC Composite Slabs

A lightweight composite bridge deck system composed of steel orthotropic deck stiffened with thin Ultra-High Performance Concrete (UHPC) layer has been proposed to eliminate fatigue cracks in orthotropic steel decks. The debonding between steel deck and UHPC layer may be introduced during construction and operation phases, which could cause adverse consequences, such as crack-induced water invasion and distinct reduction of the shear resistance. The piezoelectric lead zirconate titanate (PZT)-based technologies are used to detect interfacial debonding defects between the steel deck and the UHPC layer. Both impedance analysis and wave propagation method are employed to extract debonding features of the steel-UHPC composite slab with debonding defect in different sizes and thicknesses. Experimental tests are performed on two steel-UHPC composite slabs and a conventional steel-concrete composite deck. Additionally, an improved Particle Swarm Optimization (PSO)-k-means clustering algorithm is adopted to obtain debonding patterns based on the feature data set. The laboratory tests demonstrate that the proposed approach provides an effective way to detect interfacial debonding of steel-UHPC composite deck.

Thermal performance of composite slabs with profiled steel decking exposed to fire effects

This paper presents a systematic investigation of the influence of various parameters on the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects. The investigation uses a detailed finite-element modeling approach that represents the concrete slab with solid elements and the steel decking with shell elements. After validating the modeling approach against experimental data, a parametric study is conducted to investigate the influence of thermal boundary conditions, thermal properties of concrete, and slab geometry on the temperature distribution within composite slabs. The results show that the fire resistance of composite slabs, according to the thermal insulation criterion, is generally governed by the maximum temperature occurring at the unexposed surface of the slab, rather than the average temperature. The emissivity of steel has a significant influence on the temperature distribution in composite slabs. A new temperature-dependent emissivity is proposed for the steel decking to give a better prediction of temperatures in the slab. The moisture content of the concrete has a significant influence on the temperature distribution, with an increment of 1 % in moisture content leading to an increase in the fire resistance of about 5 minutes. The height of the upper continuous portion of the slab is found to be the key geometrical factor influencing heat transfer through the slab, particularly for the thin portion of the slab. Heat transfer through the thick portion of the slab is also significantly affected by the height of the rib and the width at the top of the rib.