Materials [SIG]

Materials to be used in the bridge models can be defined using the parameters listed below or by importing materials from OpenBrIM’s database. For further information on importing materials, refer to this link.

Basic

Modulus of Elasticity: Young's Modulus (Elastic Modulus) of the material. This has an direct impact on both finite element analysis (FEA) and design.

Poisson's Ratio: Poisson's ratio is defined as the negative ratio of the transverse strain to the axial strain.This has a direct impact on finite element analysis (FEA) and an indirect impact on design as it can affect the analysis results, which in turn can impact the design results.

Shear Modulus: Shear Modulus of the material. When two of the three parameters (Young's Modulus, Poisson ratio, and Shear modulus) are specified, the third parameter is automatically calculated by the software when a value of 0 is entered. This has a direct impact on finite element analysis (FEA) and an indirect impact on design as it can affect the analysis results, which in turn can impact the design results.

Unit Weight [10^-3]: It is defined as the weight per unit volume of the material. This parameter is used to calculate the self-weight of elements in a static analysis and the mass due to self-weight in a dynamic analysis. If the unit weight is not entered (or entered as zero), the element is assumed to be weightless. The value entered for this field is in units of x10^-4, which means that a value of 0.15x10^-4 should be entered as 0.15. This has a direct impact on finite element analysis (FEA) and an indirect impact on design as it can affect the analysis results, which in turn can impact the design results.

Thermal Coefficient [10^-6]: The coefficient of thermal expansion is a parameter used when specifying thermal loadings for a structure. It is an optional field if there are no temperature loads present. The value entered for this field is in units of x10-6, which means that a value of 6.5x10-6 should be entered as 6.5. This has a direct impact on finite element analysis (FEA) and an indirect impact on design as it can affect the analysis results, which in turn can impact the design results.

Type[Steel/Concrete/Reinforcement Bar/Prestressing Tendon]: The type of element used for the default stress-strain curve and CEB-FIP computations. This has no impact on finite element analysis (FEA) and a direct impact on design.

Stress Strain Model (readonly): Different types of materials have their own respective stress-strain curves by default. For steel materials, a bilinear steel stress-strain curve is utilized, whereas for rebars, Menegotto-Pinto steel curves are used. For concrete, the Mander concrete curve is used, and for prestressing tendons, prestressing steel curves are used. This has no impact on finite element analysis (FEA) and a direct impact on design.

Open

Stress Strain Model of Rein. Steel → Menegotto Pinto Steel

Open

Stress Strain Model of Rein. Steel → Prestressing Model

Steel

Steel Yield Stress: This has no impact on finite element analysis (FEA) and a direct impact on design.

Steel Ultimate Stress: This has no impact on finite element analysis (FEA) and a direct impact on design.

Concrete

Concrete Strength at 28 Days: Compressive strength of concrete at day 28. This has no impact on finite element analysis (FEA) and a direct impact on design.

Time Dependent

Time Dependent Elastic Modulus[Include/Ignore]: The time-dependent modulus of elasticity is a parameter used to account for the change in elastic modulus over time due to creep and shrinkage for concrete. When the time-dependent modulus of elasticity is included, the modulus of elasticity values entered under basic tab are overridden based on the computed values. According to CEB-FIP 1990, the following parameters are used to compute the time-dependent modulus of elasticity:

1. Concrete compressive strength at 28 days (fcm)

2. Cement hardening type

3. Relative humidity and temperature during curing

4. Age of concrete at time of loading (t)

These parameters are used to calculate the elastic modulus at different times during the life of the concrete member. In OpenBrIM, all calculations are based on the secant modulus of elasticity. However, CEB-FIP computes the tangent modulus. Once the tangent modulus is obtained using the CEB-FIP procedure, OpenBrIM divides the E value by 1.05 before utilizing it in finite element analysis (FEA). To ensure that this effect is included in the analysis, both the material and stage settings should be selected to include it.

Concrete Creep Effect[Include/Ignore]: Concrete creep is a time-dependent deformation of concrete under sustained load. The CEB-FIP model considers several parameters to determine the creep coefficient, which is used to calculate the time-dependent deformation of the concrete. These parameters include the concrete compressive strength at 28 days (fcm), maximum aggregate size (Dmax), cement type and percentage of cement content, relative humidity and temperature during curing, age of concrete at time of loading (t), and applied stress level (σ). OpenBrIM monitors stress changes at each stage and calculates creep accordingly by utilizing these parameters. To ensure that this effect is included in the analysis, both the material and stage settings should be selected to include it.

Concrete Shrinkage Effect[Include/Ignore]: Concrete shrinkage refers to the reduction in the volume or size of concrete over time due to the loss of moisture. When concrete is first poured, it contains a lot of water which evaporates gradually over time causing the concrete to shrink. This can result in cracks or deformations in the concrete which can affect its structural integrity. The parameters used in CEB-FIP for concrete shrinkage are the age at loading, the age at unloading, the duration of loading, the humidity of the environment, and the type and composition of the concrete mix. Additionally, CEB-FIP also considers the influence of creep on shrinkage. To ensure that this effect is included in the analysis, both the material and stage settings should be selected to include it.

Steel Relaxation Effect[Include/Ignore]: To account for relaxation effects in tendons, time-dependent material property definitions are assigned to the relevant materials. To ensure that this effect is included in the analysis, both the material and stage settings should be selected to include it.

PT Losses from Structure[Include/Ignore]: Elastic shortening losses refer to the reduction in the length of a prestressed concrete member caused by the initial stress generated during the pre-tensioning process or other external loads that could alter the length of the member. To account for this effect in the analysis, it is essential to select both the material and stage settings that include it.

CEB-FIP 1990

Concrete Strength at 28 Days (f_cm): Mean compressive strength of concrete at the age of 28 days.

Concrete Cement Hardening Type[SL/N/R/RS]: CEB-FIP recognizes three types of cement hardening based on the rate of strength development:

1. Slow hardening cement: This type of cement hardens at a slow rate and gains strength gradually over time. It is commonly used in mass concrete structures where heat buildup is a concern.

2. Normal hardening cement: This type of cement hardens at a moderate rate and gains strength gradually over time. It is commonly used for general-purpose concrete applications.

3. Rapid hardening cement: This type of cement hardens at a faster rate and gains strength more quickly than normal hardening cement. It is commonly used in construction projects that require early strength development, such as precast concrete elements.

4. Very rapid hardening cement: This type of cement hardens at an extremely fast rate and gains strength rapidly. It is typically used for special applications, such as emergency repairs and grouting, and for high-performance concrete.

Concrete Age at Beginning of Shrinkage: Time elapsed from the moment of mixing of the concrete until the beginning of the drying process that causes shrinkage.

Steel Relaxation Class[Normal(Class 1)/Improved (Class 2)]: The relaxation behavior of prestressing steels is categorized into relaxation classes based on the relaxation at 1000 hours (p1000) for initial stresses equal to 0.6, 0.7, and 0.8 times fptk. As per CEB-FIP 1990, two relaxation classes are defined:

• Class 1 represents prestressing steel with normal relaxation characteristics for wires and strands.

• Class 2 represents prestressing steel with improved relaxation characteristics for wires and strands.

Concrete Age vs Modulus of Elasticity: Equation 2.1-57 in CEB-FIP 1990 is utilized to estimate the modulus of elasticity of concrete at an age other than 28 days. Furthermore, the user has the ability to overwrite these custom values for each specific day.

Temperature Adj. Concrete Age[Yes/No]: If the user selects "yes" to consider the impact of temperature during curing, the actual concrete age should be modified using equation (2.1-87) in accordance with CEB-FIP 1990.

Dynamics

Rayleigh Damping Mass: This is the mass term in the Rayleigh damping model and represents the mass-related damping. It is defined as a linear combination of the mass matrix and the stiffness matrix of the structure, with the coefficients of the combination chosen to give the desired damping characteristics. The damping mass term is used to model the energy dissipation due to the velocity of the structure's mass.

Rayleigh Damping Stiffness: This is the stiffness term in the Rayleigh damping model and represents the stiffness-related damping. It is also defined as a linear combination of the mass matrix and the stiffness matrix of the structure, with the coefficients of the combination chosen to give the desired damping characteristics. The damping stiffness term is used to model the energy dissipation due to the deformation of the structure's stiffness.