Overview and purpose

This test problem demonstrates how

Software formulates staged-construction analysis. Also presented are various staged-construction modeling procedures, including the placement of new joints within deformed and undeformed location where time-dependent behavior is considered. A description of how users may interpret analysis output concludes the test problem.

The test-problem model consists of a 5-story column that is constructed in 5 stages which ascend vertically. At each stage, a frame object is assigned to represent a 3.7m column segment. A load of 500kN is applied in gravity direction at the top of each segment. Five load cases were defined to illustrate the process and to evaluate construction scenario. These load cases include:

• LOAD: new joints placed in undeformed position; load applied without considering creep.

• (DEF) LOAD: new joints placed in deformed position using the ghost structure concept; load applied without considering creep.

• LOAD+CR: new joints placed in undeformed position; load applied and creep is considered.

• (DEF2) LOAD+CR: new joints placed in deformed position using a ghost structure with change modifiers; load applied and creep is considered.

• (DEF2) LOAD+CR: new joints placed in deformed position using a parallel ghost structure with change modifiers; load applied and creep is considered.

Each load case is described more fully in the sections below. Further, the attached PDF file provides additional illustrative sketches. Results for each load case were independently verified by the spreadsheet calculations in the Excel files attached.

Sketch of model and staged-construction sequence

A sketch of the construction sequence and associated loading is presented in Figure 1:

A high resolution version of Figure 1 is presented in the file attached.

Summary of deflection results

Analysis generates the deflection results which follow:

A full resolution image of Figure 2 is attached in the Excel spreadsheet.

Discussion of modeling and results for individual load cases

LOAD

• Following the default procedure, newly added joints are placed in undeformed location. This would correspond to a situation when cast-in-place concrete is placed up to the desired elevation.
• Leaving the Time Dependent Material Properties option unchecked in the Nonlinear Parameters menu keeps creep from being considered in analysis.
• In each construction stage, one story is added and then loaded.

(DEF) LOAD - using ghost structure

• An auxiliary ghost structure is used to add new joints to deformed location. This is a manual staged-construction process which requires additional stages to setup and utilize the ghost structure. This method may be applicable when fixed-length precast-column segments are erected one by one.
• Creep is not considered.
• Staged construction consists of the following stages:
  • The entire structure is first added.
  • Frame property modifiers equal to 0.0001 are applied to the entire structure to make it very flexible. This is the ghost structure.
  • Stories are added one by one in the subsequent stages by first assigning unit property modifiers to the story that is being erected. This effectively assigns the actual stiffness and activates the member before load is then applied.

LOAD+CR

• Newly added joints are placed in undeformed location.
• Creep is considered.
• Construction stages are similar to those of the LOAD load case. Please note than non-zero stage duration causes creep deformation.

(DEF1) LOAD+CR - using ghost structure

• Newly added joints are placed in deformed location.
• Creep is considered.
• The construction stages are similar to those of the (DEF) LOAD load case, but non-zero stage duration leads to creep deformation in this case.
• Please note that the age of all elements is counted from the time the entire (ghost) structure is added in the first step. The upper story columns are "activated" (by changing their modifiers from GHOST to FULL) at an older age than the lower story columns. This may underestimate the creep deformation when compared to the case where all members are activated at the same (young) age of 7 days.

(DEF2) LOAD+CR - using parallel ghost structure

• Newly added joints are placed in deformed location.
• Creep is considered.
• The staged construction was slightly modified from the (DEF1) LOAD+CR load case to model all elements being activated at the age of 7 days. This was achieved by first adding the entire ghost structure and then by then adding the real structure, story by story, with an actual age of 7 days.
• Another approach to model that the elements are activated at the age of 7 days is to remove the ghost elements and then add the real elements in a subsequent stage. This is illustrated in the "(DEF3 LOAD+CR" load case in the model.

See Also

• Staged construction in buildings test problem

Attachments

• [SAP2000 V12.0.2 model |Staged construction of five-story column^SAP2000 V12.0.2 model.zip] (zipped .SDB file)
• [Hand calculations and sketches |Staged construction of five-story column^Hand_calculations_and_sketches.pdf] (PDF)
• [Spreadsheet calculations to verify SAP2000 results |Staged construction of five-story column^Verification using spreadsheet.zip] (zipped Excel file)
• [Tabulated summary of SAP2000 results |Staged construction of five-story column^Tabulated summary of SAP2000 results.zip] (zipped Excel file)