Purpose of the Study To minimize the structure depth of the new bridge carrying SH92 over the UPRR, a straddle beam was utilized. Due to the length and heavy loading, the straddle beam was post-tensioned, which required the evaluation of the beam in all stages of construction and loading. Since the beam was constructed in multiple concrete pours, it was important to consider locked-in stresses, in addition to the effect of the time-dependent effects of creep and shrinkage of the concrete, along with the relaxation of prestressing steel.
Purpose of the Seminar The work required consideration of multiple concrete pour (locked-in stress), time-dependent effect of compressive strength, creep and shrinkage, relaxation of prestressing steel, and various parameters including PT losses. In midas Civil, the construction stage analysis is easily set up together with the prestressing loading, time dependent material definition, and related group definitions to consider all of the above. Also, midas Civil provided flexible work environment for the speaker to customize the structure geometry, property, pouring sequence, etc. The speaker will go through how he utilized midas Civil for this project, specifically for the post-tensioned beam design.
Highlighted Features of midas Civil Flexible modeling One of the major strength of midas Civil is easy modeling. Using the regular functions in midas Civil, the customized beam geometry, pouring sequence and property was reflected in great detail. The powerful graphic user interface and tree menu especially helped in clearly visualizing the overall condition and details of each stage set up.
Concrete pouring sequence (with locked-in stress considered) The construction stage analysis can be set up to reflect prestressing, concrete pouring, and aging details.
Time-Dependent Effect of Creep & Shrinkage (Age Consideration) Use built in CEB-FIP / ACI / AASHTO database to create the creep/shrinkage function. The time-dependent material function will progress aligned with the construction stage analysis duration set up.
Detailed PT loss results for each construction stage (Approximate Loss Estimate as per AASHTO available) For each stage, the results can be reviewed in details as: Stress after immediate loss, elastic deform loss, creep/shrinkage loss, relaxation loss, stress after all loss, tendon elongation, element elongation, and time-dependent loss graph for each stage and each tendon strand.
Design of Straddle Beam using Spreadsheet - One tab for each construction stage considering concrete aging additional load placing - Significant time investment required (to consider locked-in stresses and estimate PT losses over time) - Obtain design based on the summary sheet - Various aspects of calculations needed to be verified (friction losses, etc.) which were difficult or impossible to directly program