ETL 1110-2-365
31 Aug 94
ANNEX 1: NONLINEAR, INCREMENTAL STRUCTURAL
ANALYSIS (NISA) DURING FEASIBILITY PHASE
A1-1. Purpose
A1-4. Material Properties
A NISA is usually performed during preconstruction
Test results for concrete mixtures will probably not
engineering and design (PED). However, if an
be available for performing a NISA during feasibility.
unprecedented structural configuration is being pro-
Material properties should be selected by the design
posed, it may be necessary to perform a NISA during
team based on previous test results from other pro-
the feasibility phase to identify requirements for
jects and adjusted for probable conditions on the new
unusual construction procedures which will signifi-
project. Properties should be consistent with a single
cantly affect project costs. The design team must
concrete mixture. Due to the uncertainty about pro-
determine the need for a NISA as early as possible
ject specific materials, properties selected for use
should include a bandwidth of +30 percent from the
during the feasibility phase. This is necessary to
expected value. This applies to values for creep,
allow results of the NISA to be incorporated into the
shrinkage, and adiabatic temperature rise.
Feasibility Report.
A1-5. Evaluation of Results
A1-2. Scope of Analysis
Results should be evaluated in terms of acceptable
A NISA during feasibility studies is nearly identical
cracking or cracking potential. The purpose of the
to a NISA during PED. However, during feasibility
analysis is to determine whether special, costly con-
studies the objective is limited to determining signi-
struction procedures are required. Therefore, there is
ficant impacts on project cost due to special con-
no specific evaluation standard for a NISA during
struction procedures. Approximate results may be
feasibility. If the analysis shows minor cracking or
adequate to define the magnitude of the cost impact.
low cracking potential, normal construction proce-
Therefore, the scope of the analysis may be simpli-
dures are likely to suffice and usual cost estimates
fied. This should not usually require numerous runs
and contingencies are satisfactory. If cracking exists
with multiple parameter combinations. This annex
or cracking potentials are high, higher contingencies
identifies the reduced requirements for NISA during
should be used for concrete costs to represent unde-
feasibility studies.
termined special procedures. If cracking is severe,
additional NISA investigation may be needed to iden-
A1-3. Parametric Combinations
tify the type and magnitude of design or construction
procedure changes needed to provide acceptable
performance.
Analysis should include only material parameter
combinations 1 and 3. Combination 3 is usually the
set of properties which produces the critical results.
A1-6. Report
Results from combination 1 should be available for
comparison with combination 3 to help evaluate the
The NISA study and results should be described in a
sensitivity of results to effects of creep and shrinkage.
section of the engineering appendix to the Feasibility
This knowledge may be necessary for selection of
Report and not in a separate report. The information
appropriate contingencies in the baseline cost esti-
should include input data such as geometry, finite
mate. Two different construction start dates should
element model, material properties, parameter combi-
be analyzed, using extreme ambient temperature
nations, loads, ambient temperature, film coefficients,
conditions. Other parametric studies may be appro-
etc. Plots of results should be included to illustrate
priate, but the number should be limited.
A1-1
Previous Page
