Thermal Stress Analysis for Durable Bridge Substructures
Prediction of early-age temperatures, thermal stresses and cracking risk in footings, pier columns, pier caps, abutments and wingwalls, from the concrete mix design to the completed placement.
Concrete Placement
A reinforced footing, 30 × 24 × 8 ft, is placed on a compacted subbase in one continuous placement. Cement hydration begins to release heat immediately after placement.
Insulation
The formwork remains in place and insulating blankets cover the top surface. Reducing the heat loss maintains the surface temperature close to the core temperature and keeps the temperature difference within the limits of the thermal control plan.
Temperature Development
The heat of hydration is generated faster than it can be dissipated through a section of this thickness. The core temperature approaches 150 °F by the third day, the insulated surface remains within 20 °F of the core, and heat is conducted from the base into the subgrade.
Expansion and Restraint
The core expands while the cooler outer concrete restrains it. This internal restraint places the core in compression and the surfaces in tension.
Cracking at the Coldest Hours
The forms and blankets are removed at dusk on the third day. The ambient temperature falls toward 34 °F and the temperature difference between the core and the top surface exceeds 45 °F. At approximately 4 AM the tensile stress exceeds the tensile strength and cracks form near the edges of the top surface.
Predicted Before Placement
The analysis determines the time and location of cracking before placement, so that the mix design, the insulation and the formwork removal schedule can be revised in the thermal control plan.
What is Mass Concrete?
“Any volume of concrete with dimensions large enough to require that measures be taken to cope with the generation of heat from the hydration of cement and attendant volume change to minimize cracking.” American Concrete Institute (ACI)
Concretetherm aims to improve the performance, safety, and durability of mass concrete bridge substructures.
How Do Thermal Stresses Develop?
- In mass concrete structures, the temperature rise caused by cement hydration can be significant, leading to internal thermal expansion.
- At the same time, heat is rapidly dissipated from the exterior surfaces, resulting in large temperature gradients.
- These gradients induce tensile stresses at the concrete surface.
Apply the available tools to evaluate thermal loading and the resulting maximum tensile stresses in mass concrete.
What is Thermal Cracking?
- When the thermal stresses exceed the concrete’s tensile strength, cracking is highly possible.
- Thermal cracking compromises durability, and accelerates reinforcement corrosion.
- Thermal cracking can be mitigated by controlling temperature differentials through improved mix design, effective insulation, and proper formwork removal timing.
- Accurate material modeling and 3D thermal–stress modeling are essential for the estimation of thermal stress magnitude and cracking prevention.
Using 3D numerical analysis, cracking risks can be investigated and therefore prevented.
3D Finite Element Modeling
3D Transient Thermal Modeling
- A 3D transient thermal model analyzes time‑dependent heat transfer inside a structure.
- It calculates how temperature rises, falls, and spreads due to conduction, convection, and radiation.
- This type of model is used when thermal conditions are not steady and must be tracked dynamically to identify hot spots, cooling rates, and thermal gradients.
3D Thermal Stress Modeling
- A 3D thermal stress model uses temperature data, often from a thermal simulation, to determine how a structure expands, contracts, or warps due to heating and cooling.
- It calculates resulting stresses, strains, and potential failure points.
Explore the Tools
From the concrete’s material properties to a full 3D thermal stress analysis of the substructure.
Material Modeling
Heat of hydration, adiabatic temperature rise, compressive strength and elastic modulus, plus the on-site insulated cube for concrete as delivered.
Open
Mesoscale Virtual Lab
Cylinders, cubes and prisms built stone by stone, then cooled, heated, loaded and broken: conductivity, CTE, stiffness, strength and cracking of a mix before it is batched.
Open
Thermal Stress Analysis
3D temperature and early-age stress analysis of footings, piers, caps and abutments, with cracking risk.
OpenLatest Mass Concrete Publications
Loading the latest publications…