Discrete element framework for modeling tertiary creep of concrete in tension and compression

Abstract

In this contribution, a computational framework for the analysis of tertiary concrete creep is presented, combining a discrete element framework with linear visco-elasticity and rate-dependency of crack opening. The well-established Lattice Discrete Particle Model (LDPM) serves as constitutive model. Aging visco-elasticity is implemented based on the Micro-Prestress-Solidification (MPS) theory, linking the mechanical response to the underlying physical and chemical processes of hydration, heat transfer and moisture transport through a multi-physics approach. The numerical framework is calibrated on literature data, which include tensile and compressive creep tests, and tests at various loading rates. Afterwards, the framework is validated on time-to-failure tests, both for flexure and compression. It is shown that the numerical framework is capable of predicting the time-dependent evolution of concrete creep deformations in the primary, secondary but also tertiary domains, including very accurate estimates of times to failure. Finally, a predictive numerical study on the time-to-failure response is presented for load levels that can not be experimentally tested, showing a deviation from the simple linear trend that is

Creep rate based time-to-failure prediction of adhesive anchor systems under sustained load

“…After discussing basic features of time to failure tests in section 2 and introducing the formulation of the criterion in section 3, the application of the criterion is investigated using the authors own data only in section 4. Finally, following the Miyano approach [25], the stress versus time to failure curve is reconstructed in section 6, verifying the two domain curve that was introduced in [18,11] in a phenomenological manner. Therefore, an appropriate function relating the creep rate to the remote stress is necessary.…”

“…Nevertheless, no conclusion on the shape of the stress versus time to failure curve was made. Ninčević et al [18] followed the findings of Boumakis et al [11] and proposed a sigmoid stress versus time-to failure curve based asymptotic matching, i.e. imposing the physically reasonable behavior for high loads approaching the short-term capacity or low loads.…”

“…The aforementioned method has the advantage of simplicity as a sole pass/fail method. The method is also conservative since the expected failure displacement would be larger than δ s , since it follows the post-peak softening branch of the short term test as showed in [10,11,12]. On the other side, the extrapolated displacement δ t is sensitive to the selected creep function as pointed out in [4,13].…”

Consistent Time-to-Failure Tests and Analyses of Adhesive Anchor Systems

“…For very short load durations approaching t = 0 the model predicts relative sustained load levels larger than 1.0, i.e. sustained load strengths that exceed the short-term strength [21]. On the other hand, the logarithmic model will predict finite failure times also for very low load levels, and even for unloaded specimens since the regression line will intersect the abscissa.…”

“…The introduced sigmoid function for the stress versus time to failure plot is a non-linear function in logarithmic time. It is well known that the relationship between stress and TTF is characterized by more than one domain [21], which can not be captured by a single linear function. As discussed for the Powell-Eyring model, the proposed sigmoid function approaches the "true" asymptotic behavior for high (horizontal asymptote at 100%) and low stress levels (horizontal asymptote at the threshold to damage development The data obtained from the sustained load tests at 85% (marked with stars) are excluded from the fit, and were used to validate the extrapolation method.…”