Recommendations for verifying lateral stability of precast beams in transitory phases

Abstract

ResumoThis paper presents recommendations for security check of precast beams in transitory phases, compare results of parametric analyzes with national and international code recommendations and confront the formulations used for the calculation of critical load of lateral instability. In transport and lifting phases, precast beams are susceptible to loss lateral stability because the established supports provides little restriction to the element rotate on its principal axis and move laterally. To recommend limits of slenderness, parametric analysis are performed using formulations based on bifurcacional instability, including eigenvalue problems with the finite element method. The results show that the safety limits for I beams and rectangular beams are different. For the analyzed cases and with reference to beam slenderness equation used by fib Model Code [13], the limit determined for rectangular beams would be 85 and for I beams 53, which could be taken as 50, as recommended by the code. Within the analyzed cases of I beams, only the fib Model Code [13] recommendation attend the slenderness limit for transitory phases.Este artigo objetiva apresentar recomendações para a verificação da segurança de vigas pré-moldadas em fases transitórias, comparar resultados de análises paramétricas com recomendações de normas nacionais e internacionais e confrontar as formulações utilizadas para o cálculo da carga crítica de instabilidade lateral. Nas fases transitórias de transporte e içamento, as vigas pré-moldadas são suscetíveis à perda de estabilidade lateral, porque a vinculação estabelecida oferece pequena restrição ao elemento de girar em torno de seu eixo e deslocar-se lateralmente. Para recomendar limites de esbeltez são realizadas análises paramétricas utilizando formulações baseadas em instabilidade bifurcacional, incluindo problemas de autovalor com o método dos elementos finitos. Os resultados mostram que os limites de segurança para vigas I e retangular são diferentes. Para os casos analisados e tomando como referência a equação de esbeltez de viga utilizada pelo fib Model Code [13], o limite determinado para vigas retangulares seria de 85 e para vigas de seção I seria de 53, o que poderia ser tomado igual a 50, como recomendado pela norma. Dentre os casos analisados de vigas I, somente a recomendação do fib Model Code [13] atende o limite de esbeltez para fases transitórias.Palavras-chave: instabilidade lateral de vigas, concreto pré-moldado, içamento, transporte, esbeltez.

Optimum design of precast and prestressed beams with focus on CO2 emission reduction

“…The transient phase is inherent to precast concrete and is considered an intermediate stage to the use of the structure and can become critical, leading the element to a limit [26]. According to Lewick [27] and Krahl et al [28], the different phases must be considered, such as manufacturing in the course, storage, transport, and placement of the elements.…”

Rollover stability of precast concrete beams supported by elastomeric bearing pads

“…There are two possible solutions to take this into account in the stability analysis. The solution of Southwell [15], equation (11).…”

“…The main transitory situations that these elements are subjected are lifting, transport and when supported only by bearing pads. The first two conditions were widely studied and have consolidated analytical solutions, [1], [8]- [10], as presented in recent research Krahl et al [11]. However, the last phase is an open field yet, because the difficulty in develops experimental research.…”

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

“…KRAHL, 2014), and even reported, there are some papers and technical reports that care about the subject. The understanding of the possible causes of collapses can help significantly possible code recommendations and the development of safety measures to decrease the risks in such construction stages.…”