Modelling the Fire Resistance of Prestressed Concrete Floors using Multi-Spring Connection Elements

Abstract

Despite big advances in analytical modelling of the performance of structures exposed to fire, there has been difficulty in modelling the fire performance of precast prestressed concrete floor slabs in multi storey buildings. The fire resistance of these floor systems is heavily influenced by the end connections and the stiffness of the surrounding structure, both of which must be considered in any analysis.Previous "traditional" studies have modelled the floor slabs with beam or shell elements in which the end nodes share the nodes of the beam elements representing the supporting beams. This is acceptable for cast-in-situ or precast flooring system without prestressing, but leads to a major problem for precast prestressed flooring systems where the steel tendons terminate at the end of the flooring units, because the approach of sharing nodes of the supporting beam and floor assumes that these tendons are anchored into the supporting beams.In order to solve this problem, a "multi-spring" connection element has been developed. The multi-spring connection element consists of several parallel axial springs sandwiched between two rigid plates. Each spring represents either a steel reinforcing layer or a segment of concrete in the floor cross-section. The concrete springs have compression-only properties. This multi-spring connection is placed between the end nodes of the floor and the nodes of the supporting beam. With this element, it is possible to terminate the prestressing tendons at the end node of the floor elements and to anchor only the topping reinforcement into the supporting systems predicted using the traditional approach and the newly developed multispring connection, with applications to different forms of precast concrete floors in multi storey buildings.

Modeling the response of precast, prestressed concrete hollow-core slabs exposed to fire

“…Breccolotti et al, 8 Fellinger et al, 12 Dotreppe and Franssen, 17 Chang et al, 18 and Min et al 19 conducted numerical studies on precast, prestressed concrete hollow-core slabs in fire. Basically, the finite element approach was used for numerical studies, with the slab being discretized using linear, plane, and solid elements.…”

“…Basically, the finite element approach was used for numerical studies, with the slab being discretized using linear, plane, and solid elements. 8,12,[17][18][19] These approaches for evaluating the fire resistance of precast, prestressed concrete hollow-core slabs typically comprised the following analytical steps, conducted at various time steps until failure occurred:…”

Prestressed hollow-core slabs performance at high temperatures- A review

“…Furthermore, there aren't any restrictions on the characteristics that may be found in numerical modelling in order to analyse the behaviour of HCS more thoroughly. There have been few numerical investigations into the FR of HCS, with the majority of these studies employing finite element-based models such as SAFIR [25,27], DIANA 2000 [8,26], FIRES T3 [10], COMSOL [28], ANSYS [19], or the new 2-phase computational model [29]. For the purpose of verifying the experimental tests, the ISO 834 standard was used.…”

Fire behavior of shallow prestressed hollow core slabs from computational modeling

“…There are several studies in the literature about reinforced concrete beams and columns exposed to fire [10][11][12][13], as well as steel-concrete composite structures [14][15][16][17]. There are also several studies about the behavior of hollow core slabs exposed to fire, either by tests or computational modeling [18][19][20][21][22][23][24][25][26][27]. However, most of these studies consider hollow core slabs with high height.…”