Conference Agenda

The study quantitatively investigates to which extent the hydration of ordinary Portland cement (OPC) contributes to the early-age strength evolution of cement pastes produced with binders containing OPC and limestone (acronym LPC) as well as OPC, limestone, and calcined clay (acronym LC3), respectively. A multiscale strength model for OPC pastes is adapted to binary and ternary mixtures made of CEMI, limestone, and calcined clay. To this end, limestone and calcined clay are introduced as chemically inert spherical inclusion phases which are embedded (next to reactive cement clinker grains) in the hydrate foam matrix. The volume fractions are calculated using Powers’ hydration model extended towards consideration of the two additional inert inclusion phases. Elastic phase properties are taken from the literature. The strength predictions for the OPC, LPC, and LC3 pastes are checked against strength values obtained from compressive strength testing during the first week after paste production. The study shows that the OPC hydration plays a governing role when it comes to the early-age strength development of the LPC and LC3 pastes.

Many existing concrete structures have been fulfilling their purpose for several decades, but they may no longer meet current structural safety standards due to various factors. This fact highlights the urgent need for innovative solutions to ensure the durability and performance of these structures under increasing load and changing environment. Digital twins can indeed provide very effective solutions in various contexts. A digital twin is a virtual representation of a physical object or system that is used to simulate, predict, and optimize performance. By creating a digital twin, one can analyze data and monitor systems to prevent problems before they occur, develop new opportunities, and plan for the future by using simulations. In this work, we focus on the load-bearing behavior of a specially reinforced existing pier of the Jauntal Bridge in Carinthia (DT Physical Model). This behavior is virtually simulated using a non-linear finite element model (DT Virtual Model). The aim is to draw conclusions about the constantly changing load conditions by observing the development of cracks and the geometric deformations (DT Monitoring, e.g., via orthographic and radar interferometry) and thus to make statements about the constantly fluctuating safety level and the fluctuating service life. Based on these findings, it should be possible to optimize the existing verification formats and the arrangement of the reinforcement measures, particularly the prestressing bars and the interaction between new and old concrete at the pier heads. Consequently, this would allow for a direct assessment of the constantly fluctuating loads and safety levels.

Many existing concrete structures have been fulfilling their purpose for several decades, but they may no longer meet current structural safety standards due to various factors. This fact highlights the urgent need for innovative solutions to ensure the durability and performance of these structures under increasing load and changing environment. Statistical study has to be included to consider uncertainties, also safety formats approaches can be utilized. The aim of this research is to show how a procedure for quality control and safety assessment of 100 m high concrete piers was developed based on non-linear finite element analysis and digital twin technology considering uncertainties involved. Piers are parts of Jauntal bridge, a 60-year-old, 450 m long railway bridge that has been equipped with a new bridge deck. The purpose of the study was to investigate structural safety, serviceability, durability, and remaining service life of the bearing socket and pier systems equipped with a new confinement concept. The research uses a reliability-based approach utilizing advanced probabilistic methods, based on reliability index determination and efficient safety format approaches. Standard ECoV and Eigen ECoV methods were employed for an estimation of mean values and standard deviations for all steps of the finite element analysis, assuming two limit cases of probability distribution of resistance – Gaussian and Lognormal. The stochastic model contains only the 4 most significant random variables of the computational model representing the material characteristics of the concrete pier.

In large buildings, the combined application of long-span prestressed concrete beams and short-span reinforced concrete beams is common. Such structures are designated as local prestressed concrete (LPC) structures. LPC structures could be classified into two types: unbonded local prestressed concrete (UBLPC) structures and bonded local prestressed concrete (BLPC) structures. Nevertheless, the crack patterns of LPC structures under progressive collapse remains unclear. The bond effect between prestressed tendon and concrete on crack development and load-carrying capacity is yet to be elucidated. Therefore, this paper tested the progressive collapse resistance of BLPC and UBLPC substructures. The results indicated that LPC substructures exhibited the resistance mechanism comprising two distinct stages: beam-beam stage and beam-link stage. A main crack appeared at the junction of the reinforced and non-reinforced regions of the longitudinal rebar in long-span beam, with surrounding clusters of cracks. The cracking at the ends of short-span beam was significant. Mechanistic analyses revealed the bond effect on crack patterns. Theoretical derivation demonstrated that bonded prestressing provided higher resistance than unbonded prestressing. However, bonded prestressed tendon was more prone to fracture. This study could inform the design of LPC structures against progressive collapse.