Overview and Purpose

The purpose of this test problem is to illustrate how stage construction is handled in SAP2000 and how various aspects of stage construction (such as placing new joints to deformed or undeformed location; considering time dependent behavior) can be modeled and how to interpret the results.

The model consists of a 5-story column that is constructed in 5 stages, from the bottom up. In each stage, a frame member representing a 3.7 m long segment of the column is added and a load of 500 kN is applied to the top of the segment in gravity direction. The following 5 load cases were setup to evaluate different construction scenarios and to illustrate how SAP2000 handles the staged construction definition:

• LOAD: place new joints in undeformed position, apply load only and do not consider creep
• (DEF) LOAD: place new joints in deformed position using [ghost structure] concept, apply load only and do not consider creep
• LOAD+CR: place new joints in undeformed position, apply load and consider creep
• (DEF) LOAD+CR: place new joints in deformed position using ghost structure with change modifiers operation, apply load and consider creep
• (DEF2) LOAD+CR: place new joints in deformed position using ghost structure with change modifiers, remove structure and add structure operations, apply load and consider creep

Please refer to the sections below for a more detailed description of each load case. Also refer to the attached PDF file with illustrative sketches. Results for each load case were independently verified by spreadsheet calculations, please see the attached Excel files.

Sketch of Model and Staged Construction Sequence

(Please see the attached PDF file for a high resolution of the below sketch.)

Summary of SAP2000 Deflections

(See the attached Excel file for a full resolution image.)

Discussion of Modeling and Results for Individual Load Cases

LOAD

• Newly added joints are placed in undeformed location (this is the default way SAP2000 handles construction stage analysis). This would correspond to a situation when cast-in-place concrete is placed up to the desired elevation.
• Creep is not consider by keeping "Time Dependent Material Properties" option unchecked on the Nonlinear Parameters form.
• In each construction stage, one story is added and then loaded.

(DEF) LOAD

• Newly added joints are placed in deformed location by using an auxiliary [ghost structure] (this is not the default way SAP2000 handles staged construction and it requires some additional stages to setup and utilize the ghost structure.). This would correspond to a situation precast segments of the column with a fixed length are being 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 first assigning unit property modifiers to the story that is being erected (this effectively assigns the actual stiffness and activates the member) and then load is applied.

LOAD+CR

• Newly added joints are placed in undeformed location.
• Creep is considered.
• Construction stages are similar as for the "LOAD" load case. Note than nonzero duration of the stages causes creep deformation.

(DEF) LOAD+CR

• Newly added joints are placed in deformed location.
• Creep is considered.
• The stages of the staged construction are similar to the "(DEF) LOAD" load case, but nonzero duration of the stages leads to creep deformation in this case.
  Note that the*age of all elements is counted from the time when the entire (ghost) structure was added in the first step. This upper story columns are activated at an older age than the lower story columns. This may underestimate the creep deformation compared to the case when all members activated at the same (young) age, say 7 days.

(DEF2) LOAD+CR

• Newly added joints are placed in deformed location.
• Creep is considered.
  The staged construction was slightly modified from the "(DEF) LOAD+CR" load case to model*all elements being activated at the age of 7 days. The modification involved removing and then adding members with the age of 7 days prior to activating the members by changing their property modifiers from 0.0001 to 1.

See Also

• [tutorials:Staged construction in buildings]

Attachments

• [Hand calculations and sketches|^Hand_calculations_and_sketches.pdf] (PDF File)
• [Spreadsheet calculations to verify SAP2000 results|^Verification using spreadsheet.zip] (Zipped Excel file)
• [Tabulated summary of SAP2000 results|^Tabulated summary of SAP2000 results.zip] (Zipped Excel file)
• [SAP2000 V12.0.2 model|^SAP2000 V12.0.2 model.zip] (Zipped SDB File)