Behavior of Steel–Concrete Partially Composite Beams Subjected to Fire—Part 1: Experimental Study

Partially composite steel–concrete beams are commonly used in building construction, and so the behavior of such beams in fire is an important problem. This paper presents the results of an experimental investigation on the response of two composite beam specimens subject to fire exposure. The two specimens were nominally identical, except for the shear connection ratio. Based on room temperature calculations, one specimen was designed as fully composite, and the second was designed as partially composite with a 50% shear connection ratio. The concrete slab for each specimen was constructed with a flat steel deck and reinforcement was provided by a reinforcing bar truss. Both specimens were subject to a constant vertical load applied at four locations along the span and tested in a furnace with an ISO-834 standard fire. Both specimens achieved large deflections associated with flexural yielding of the composite beams and exhibited measured flexural capacities larger than predicted from Eurocode 4. Based on test measurements, the shear connection ratio had a significant influence on interface slip and uplift behavior of concrete slabs. Failure of the specimens was defined when the maximum deflection reached span/30. The fire exposure time needed to reach this definition of failure was nearly the same for both specimens, and was 51 min for the fully composite beam and 49 min for the partially composite beam. A companion paper considers the degradation of material properties with temperature and slips behavior of shear connectors at elevated temperatures and also provides an analytical approach to predict fire response of steel–concrete partially composite beams.     

Behavior of Steel–Concrete Partially Composite Beams Subjected to Fire—Part 2: Analytical Study

This paper presents the development of an analytical model of steel–concrete partially composite beams subjected to fire. The model includes consideration of temperature dependent material properties, temperature dependent interface slip between concrete and steel, non-uniform temperature distributions throughout the cross-section and the effect of different rates of thermal expansion at the concrete–steel interface. Model predictions showed good agreement with the results of fire tests on two composite beams reported in an earlier companion paper as well as with limited experimental data published in literature. An extensive parametric study was undertaken by using the proposed model. Parameters considered in this study included geometric dimensions of the composite beam, material grades of steel and concrete, shear connection ratio, reinforcing steel ratio in the concrete slab, and load level on the beam. The parametric study clearly shows that shear connection ratio and load level significantly influence the fire performance of partially composite beams. The critical temperatures with shear connection ratio of 50%, 75% and 100% are 645°C, 602°C and 548°C, respectively, under load level of 0.6. The critical temperatures under load ratio of 0.5, 0.6 and 0.7 are 468°C, 553°C and 633°C respectively, with a shear connection ratio of 50%.     

Numerical Studies on Fire Resistance of Prestressed Continuous Steel–Concrete Composite Beams

Fire Technology - Prestressed continuous composite beams (PCCBs) have been widely used in constructions. While the open literature contains notable works that examine the behavior of PCCBs at...     

Effect of Rib Geometry in Steel–Concrete Composite Beams with Deep Profiled Sheeting

International Journal of Steel Structures - Presented are the results from a finite element model of steel–concrete composite beams with deep decks and a comparison with various...     

Predicting the Fire Resistance of Wood–Steel–Wood Timber Connections

This paper presents an investigation on the fire performance of wood–steel–wood timber connections with slotted-in steel plates. In the first part, a three-dimensional thermal model was employed that uses the finite element method to analyze heat transfer within timber connections exposed to the standard fire. The temperature-related properties were obtained from the literature and imported into the thermal model. A validation of the proposed thermal model was achieved by comparing predicted temperatures with experimental results. In the next phase, a reduction in the embedding strength method was adopted to estimate the load-carrying capacity of connections in fire. Based on the temperature profiles within the connection calculated by the thermal model, the reduction of the embedding strength was determined and used to calculate the load capacity at elevated temperatures. Furthermore, a formula was proposed to evaluate the fire resistance rating of timber connections and compared with the results of fire resistance tests. The parameters considered included the load level, fastener diameter and wood member thickness.     

Tension–Shear Experimental Analysis and Fracture Models Calibration on Q235 Steel

International Journal of Steel Structures - Tension–shear loading is a common loading condition in steel structures during the earthquake shaking. To study ductile fracture in structural...     

Statistical Analysis and Review of Fire Incidents Data of Greece,with Special Focus on Residential Cases 2000–2019

Fire Technology - Urban fires are annually responsible for heavy financial, property, business and life loss. The present study attempts to assess from a quantitative and qualitative perspective...     

Behavior of FRP–concrete–steel double skin tubular members under lateral impact: Experimental study

In this paper, an experimental investigation on the impact performance of FRP–concrete–steel double skin tubular members is presented. Twenty-four tests were carried out to examine the failure modes and the time histories of the impact forces, lateral deformations and strains. The effects of the impact energy and number of FRP layers on the impact behavior of the double skin tubular members were discussed. The results show that FRP–concrete–steel double skin tubular members behave in a ductile manner; there is a long stabilized stage of impact forces and the residual deformation mainly results from the cracking of FRP and concrete, as well as the overall bending deformation. The confinement of the outer FRP layers in the hoop direction to the sandwiched concrete in the composite members is small during the whole impact process. However, increasing the number of the outer FRP layers is somewhat beneficial to improve the dynamic resistance ability. The effect of the impact energy on the dynamic response of the composite members is significant. The difference between the FRP–concrete–steel double skin tubular members, concrete filled double skin steel tubes and concrete filled steel tubes is discussed based on the test results in this paper.     

A Study on People’s Attitude to the Use of Elevators for Fire Escape

Currently, elevators are not considered as a proper means of escape in fires and people have been educated and trained to use staircases for fire escape. However, it is difficult for all the occupants to evacuate only by staircases timely and safely in super high-rise buildings, especially for the old and disabled. Considering the fact that super high-rise buildings are constructed in increasing numbers in many Asian cities, it becomes much more necessary to reconsider the use of elevators for emergency escape. Besides a mechanically safe elevator system, people’s cooperation is of critical importance to assure an efficient egress process. To explore people’s attitude to the use of elevators for fire escape in high-rise buildings and the diversity based on demographics, a study was conducted via face-to-face interviews in two different cities of China. Respondents’ demographics and their responses to hypothetical fire scenarios were collected via a set of structured questions. The results showed that most people would consider using elevators for fire escape in super high-rise buildings. The main influencing factors of their attitude were firemen’s instruction and the height of their location in the building. Statistical diversity was found based on demographics. These results indicated that people’s attitude to elevator evacuation was positive and further study should be very important.     

Experimental investigation on seepage erosion of the soil–rock interface

Bulletin of Engineering Geology and the Environment - Internal erosion under seepage flow affects the hydraulic and mechanical behavior of the soil, which is one of the most important factors of...     

Experimental studies on the extinction of methane/air cup-burner flames with gas–solid composite particles

Fire suppression effectiveness of gas–solid composite particles consisting of 2-bromo-3,3,3-trifluoropropene (BTP) and zeolite 13X was evaluated on a cup-burner apparatus with coflowing methane/air flame. A series of composite samples with the weight concentration of BTP (ω) varying from 1.0 to 12.0% were tested. For comparison, extinction measurements were also conducted using neat BTP and zeolite 13X, respectively. Results indicated that the composite particles on a mass basis were much more effective than that of BTP and zeolite 13X used alone. A synergistic effect was exhibited by the BTP/zeolite 13X composites, which was affected by the ω values. Furthermore, significantly reduced HF concentrations (<70 ppm) were detected in the suppression tests with the composite particles, in comparison to that of neat BTP (1436 ppm). The composite particles extinguished the flame through a blowoff process, in which the flame base oscillated, detached from the cup-burner rim and extinguished eventually. Mechanism of the composite particles in suppressing the cup burner flame was studied.     

Experimental investigation on aggregate interlocking concrete prepared with scattering–filling coarse aggregate process

To secure good flowability and segregation resistance of the fresh concrete mixture, the volume fraction of the coarse aggregate in the conventional plastic concrete is controlled at a relatively low level. A new type of coarse aggregate interlocking concrete was prepared with a new invented concrete placing method named as scattering–filling aggregate process. The strength of concrete prepared with this method obviously increases whereas the shrinkage ratios of them decrease significantly with the extra adding aggregate volume ratio from 10% to 30%. These concretes with high strength and low shrinkage can be prepared with much lower cement dosage compared to the conventional process. The SEM observation indicated that the interfacial transition zones at the interface of the added aggregate are much tighter than those of the original aggregate. The interlocking and homogeneous distribution of the coarse aggregate and the water absorption of the extra added coarse aggregate contribute to the strength improvement and performance modification.     

Experimental and theoretical studies on composite steel–concrete box beams with external tendons

Composite steel–concrete box beams with and without external tendons were tested to their ultimate strength. The effects of external tendons on structural performance of composite steel–concrete beams were investigated in detail. Experimental results proved that, due to the action of external prestressing tendons, the ultimate strength of a composite steel–concrete box beam increased by 27.72%, the elastic limit of a composite steel–concrete box beam increased by 29.17%, the stiffness of a composite steel–concrete box beam increased by 54.15% at the failure state, and the deflection ductility of a composite steel–concrete box beam increased by 18.00%. The equation for estimating the stress in external prestressing tendons is established according to the relationship between the stress in external tendons, and the maximum compressive strain of concrete slab. Based on experimental results, a theoretical model for predicting the flexural resistance of composite steel–concrete box beam with external tendons is proposed. The spatial integral method, which adopts the actual stress distribution, is more rational than the conventional equilibrium rectangular stress block model, and is adopted to calculate the interior force on sections. The calculated flexural resistance based on proposed equations has a high level of accuracy, when compared with test results. Experimental and theoretical studies have demonstrated that the composite steel–concrete box beam with external tendons is a promising innovative structure that combines the merits of composite steel–concrete box beams and external prestressing tendons.     

Analysis on Extension Length of Shape Steel in Transfer Columns of SRC–RC Hybrid Structures

Seismic performance of SRC–RC transfer column was analyzed based on the experiment of 16 transfer columns specimens under low cyclic reversed loading, which mainly focus on the extension length of shape steel. Analysis of ductility, bearing capacity, energy dissipation capacity and degeneration ratio of strength were completed. Displacement ductility promotes at first and then reduces with increasing of extension length of shape steel, reaching the peak value when extension length gets close to three fifths of column height. Extension length of shape steel has little effect on bearing capacity, while energy dissipation capacity of transfer columns is influenced by many factors. Three fifths of column height is the rational extension length of shape steel, of which specimens have advanced in energy dissipation, good stability of stiffness and strength. The bond performance between concrete and shape steel decreases with the increasing of extension length of shape steel, and hence the stability of strength decreases. Minimum extension length of shape steel was confirmed and the calculation method was proposed, which is mainly used to ensure the bend yielding of shape steel at bottom section. Moment at the truncation section leads to pull-out effect of steel bars, which enhances with increasing of the moment and section ratio of shape steel. Contraflexure point is at three fifths of column height. If the shape steel extends to contraflexure point, moment of steel truncation section will reach minimum. So the reduce the concrete damage with better deformation ability and mechanical behavior of transfer column.     

Experimental investigation on adsorption capacity of ACF–methanol pairs for cooling application

Solar cooling technology is very popular among other conventional cooling technologies due to increment in global warming effects. In solar cooling technology, solar-powered adsorption refrigeration system has potential to compete with other non-conventional cooling technologies, that is, Absorption, PV-based, Waste-heat-driven and Biogas cooling. The main objective of this research work was to investigate the adsorption capacity of methanol onto activated carbon fibre in the temperature range of 15–80°C during an isobaric adsorption process. To correlate adsorption characteristics’ data of the experiment, the Dubinin–Astakhov equation is used. From a series of experiments, the maximum adsorption capacity was found to be 0.44?kg/kg of ACF by maintaining packing density of bed at 110?kg/m³. The effect of heat generator temperature on adsorption capacity is also studied in this investigation.     

Acoustical Extinction of Flame on Moving Firebrand for the Fire Protection in Wildland–Urban Interface

Fire Technology - Firebrands are a widely observed phenomenon in wildland fires, which can transport for a long distance, cause spot ignition in the wildland–urban interface (WUI) and...     

Development of a Fluid–Structure Coupling Validated with a Confined Fire: Application to Painted Caves

Fire Technology - In 1994, three speleologists discovered the Chauvet–Pont d’Arc Cave, which contains singular thermal marks on walls deep in the cavity. These alterations arose from...     

Behavior and strength of steel reinforced concrete beam–column joints with single-side force inputs

Five large-scale beam–column subassemblies were fabricated and tested under cyclic loading to investigate the behavior of SRC Type I exterior and Type II corner beam–column joints. In addition, the applicability of strength superposition method on joint shear strength was assessed. It was found that: (1) the strength superposition method was able to estimate the SRC beam–column joint shear strength with reasonable accuracy; (2) the anchorage position of beam longitudinal bars has an obvious influence on the joint shear strength and crack pattern; (3) increased depth of cross-sectional steel leads to a higher shear strength for the beam–column joint; and (4) a combination of corner stirrups and shaped steel cross-sections was able to provide sufficient lateral support to longitudinal steel bars and adequate confinement to the concrete in the joint to replace the need for closed hoops.     

Study on visible–IR radiative properties of personal protective clothings for firefighting

This work deals with the radiative properties of personal protective clothings worn during firefighting operations by firemen. Several intervention jackets are tested coming from different Fire and Rescue Services in France. The present study focuses on the spectral absorptivity of these equipments over visible–IR domains. The spectral absorptivity in the IR range is mainly responsible for the conversion of radiative transfer coming from the flame into heat flux through the protective jacket. This work shows that the mean absorptivities of different equipments are high, close to 90%, which penalizes the thermal protection. This study demonstrates that the colored textile has a weak effect on the radiative properties and then on the thermal protection. On the contrary, the dyeing mode can decrease the absorptivity, hence improving the thermal protection of jackets, a dyed jacket being more efficient in the present test than a jacket made of fibers dyed before weaving. Finally, this paper presents mean absorptivities based on Planck's averages for reference temperatures between 800 K and 1400 K, allowing to compare different personal protective clothings.