Rollover stability of precast concrete beams supported by elastomeric bearing pads

Abstract

ResumoDuring construction of precast girder bridges, there is the concern on rollover instability of the beams when exclusively supported by elastomeric bearing pads. This type of failure has been the focus of recent research due several accidents reported. However, these studies have not considered the nonlinear behavior of elastomeric bearing pads and the lift-off effect. Therefore, this paper presents a parametric study with a finite element model calibrated with experimental results, reported in the literature, through a nonlinear geometrical analysis and considering that concrete behaves linearly. Besides, the experimental results are compared to simplified approaches which account the pad nonlinear behavior and the lift-off effect by utilizing its secant rotational stiffness. From the results, the difference between the instability load from nonlinear geometrical analysis and experimental results was 8.7 %, and the simplified eigenvalue solution and experimental was 11.4 %, which was the best fit compared to the other existing analytical models. From the parametrical analysis, the instability load was considerably decreased by varying the initial lateral deflection, the skewed pad rotation, top flange width and the span of the beam.Keywords: precast beam, lift-off effect, bearing pads, rollover instability, nonlinear behavior, numerical analysis, eigenvalue analysis. Durante a construção de pontes em vigas há a preocupação com a instabilidade por tombamento de vigas quando estão sobre aparelhos de apoio. Este tipo de colapso tem sido foco de pesquisas devido a uma série de acidentes reportados. No entanto, estes estudos não têm considerado o comportamento não-linear dos aparelhos de apoio e a perda de contato entre a viga e o neoprene (lift-off). Portanto, este artigo apresenta um estudo paramétrico com um modelo em elementos finitos, calibrado com resultados experimentais da literatura, através de análise não-linear geométrica. Além disso, os resultados experimentais são comparados com modelos analíticos simplificados que levam em conta o efeito lift-off pela utilização da rigidez secante à rotação do aparelho de apoio. A partir dos resultados, a diferença entre a carga de instabilidade experimental e a obtida pela análise não-linear geométrica foi de 8.7 % e para o modelo de auto-valor simplificado foi 11.4 % que apresentou a melhor aproximação comparado a outros modelos analíticos. Das análises paramétricas, a carga de instabilidade decresceu significativamente pelo aumento do deslocamento lateral inicial, da rotação do aparelho de apoio relativa ao eixo da viga, diminuição da largura da mesa superior da viga e pelo aumento do vão.Palavras-chave: viga pré-moldada, efeito de lift-off, aparelho de apoio, instabilidade ao tombamento, comportamento não-linear, análise numé-rica, análise de auto-valor.

Numerical analysis of the effective stiffness of elastomeric bearing pads under precast beams for the limit load of lateral instability

“…Once the load-displacement curve has been obtained, according to the criterion of Consolazio, Hamilton and Beery [3], one obtains, for the relationship 1/10 of the initial slope (Figure4), a limit load of approximately 484.0 kN. This, when compared to the values from Hurff [8] (463.0 kN) and Krahl, Carrazedo and El Debs [5] (503.3 kN), results in differences of 4.5% and 3.8%, respectively. Figure 10 shows the loss of contact that occurs with the application of self-weight, before the application of load concentrated in the middle of the span, and the loss of contact through the application of the limit load.…”

“…Beam section PCI BT-54 (dimensions in mm) Source: Hurff [8] Numerical analysis of the effective stiffness of elastomeric bearing pads under precast beams for the limit load of lateral instability Hurff [8] measured the initial lateral eccentricity of the beam in the middle of the span, with an obtained value of 43.5 mm. Figure 9 presents the comparison of the experimental results from Hurff [8] to the proposed numerical model and the numerical results from Krahl, Carrazedo and El Debs [5].…”

“…Despite the high risk to worker safety and losses caused by this type of collapse, there in fact exist few experimental studies developed on the subject (CONSOLAZIO; HAMILTON; BEERY [3],HURFF; KAHN [4]). Consequently, few numerical studies have been performed to represent the behavior of long beams under rollover failure, when only supported on neoprene bearing pads (KRAHL; CARRAZEDO; EL DEBS [5]; LEE [6]; CARDOSO; LIMA [7]). However, this field of research requires greater investigation in the field of experiment, as well as numerical, in order that recommendations can be established.…”

Lateral stability of ultra-high performance fiber-reinforced concrete beams with emphasis in transitory phases

“…Also, it is known that precast elements are subjected to transitory phases, like lifting, transport and when only supported only by bearing pads, (EL DEBS, 2017). In these situations arise the concern with instability problems due to the poor constraint against toppling provided by the supports and, also, the increased slenderness provided by UHPFRC.…”

“…Precast concrete beams are susceptible to transitory stages of construction since demolding from formwork until the permanent phase. All these stages are described in (EL DEBS, 2017), which highlights the possibility of different efforts from the service stage and the importance of concrete strength at early ages. The phases that present primary concern with structural stability of beams are lifting, transport and beam supported only by bearing pads.…”