CEGE0009 GSA Assignment
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CEGE0009 Structural Design and Analysis
Assessment of an existing building using GSA
Coursework Brief
Learning objectives:
1. Practise using GSA modelling and checking FE (Finite Element) outputs
2. Understand how a reinforced concrete frame is typically modelled with FE
3. Understand how a Finite Element global structural model is used to obtain design
forces of particular members
4. Practise ultimate capacity calculations for RC members
5. Depend understanding of frame structural behaviour and checking results against a
different program
Background
Figure 1 shows a reinforced concrete frame which is the structural system supporting an
existing building in central London. The building was originally designed for residential use
which means it was designed for a live load of 1.5 kN/m2
. The building owner is now
contemplating changing the type of occupancy of the building to commercial use.
Figure 1. Reinforced Concrete Frame
Your job
As part of your tutorial group, you will be working as structural consultants to advise the
building owner (the client) on whether the proposed change of use is structurally safe or not.
CEGE0009 GSA Assignment
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As this is an existing structure, the beams and columns already have cross-section dimensions
and reinforcement detailing as given in Figure 2 and Table 1. Your task is to assess whether
the current members have sufficient capacity to resist the new anticipated design bending
moments and axial forces under the new loading condition following provisions as per BS EN
1992-1-1:2004. The allocated structural properties (geometric and material) as well as the new
imposed loads can be found in Table 1. Shear capacity and detailing will not be considered
but a shear reinforcement diameter is provided so that the position of the bending
reinforcement can be calculated.
As1 = 2H8
As2 = 4H10
As3 = 2H12
Shear stirrups H8
Reinforcement Strength,
fy = 500 N/mm2
RC specific weight: 25kN/m3
Concrete Cover = 30mm
Figure 2. Characteristics of all beam and column sections,
further information on geometry and material properties of the section can be found in Table1
GSA Modelling
Using Oasys GSA 9, you will build a wireframe model (i.e. made of 1D elements) of the whole
frame using beam elements throughout. You will use the frame dimensions and member
structural properties allocated to your group (see table p3). As per usual practice, the steel
bars are not included in FE models however the specific weight of reinforced concrete should
be used so that gravity loads include the weight of the steel reinforcement. The columns will
be clamped at their base.
The slabs will be assumed to be 2-way spanning but will not be modelled explicitly but their
load (dead+live) will be imposed on the frame using the GSA functionality called “area grid
load” (see step-by-step guide). This is effectively an external pressure applied over a specified
area. This area load is distributed on the adjacent supporting beams. The calculation is done
internally by GSA using a standard tributary area method. Once you have identified the live
load intensity for your building type, apply that on the first two floor slabs and only half of that
value on the top floor slab as this is just a roof. For the slab dead load, assume reinforced
concrete slabs with a thickness of 150 mm throughout.
Distributed (line) loads of 4kN/m should be applied on all first and second floor beams to
account for the weight of the infill walls within the frame (these are not shown in Figure 1).
Pattern loading on the first and second floor slabs should be considered for the live load for
load combination 3 (see below). For this small frame this can be done simply by changing the
magnitude of the area live load on each slab ‘manually’.
Wind load will be considered acting on the xz elevation only. The load will be applied as point
loads on that façade nodes and the magnitude of each load will be calculated by hand
CEGE0009 GSA Assignment
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assuming that each node takes the resultant of the pressure on the tributary area of the façade
(same method as column tributary area under gravity load).
The model will be analysed using a static, linear analysis. In order to identify the most critical
design internal forces that each member will experience, the following load combinations
should be defined and run in the software (following the provisions of BS EN 1990:2002):
1) Dead Load
2) Dead Load + Live Load
3) 1.35 Dead Load + 1.5 Live Load
4) 1.35 Dead Load + 1.5 Wind Load
5) 1.35 Dead Load + 1.5 Live Load + 0.75 Wind Load
More specific tasks will be required when only the wind load is acting on the frame (no gravity).
This loading scenario is unrealistic and unlikely to lead to critical design forces, it is useful for
the purpose of appreciating the magnitude and shape of the internal forces generated by wind
and to make it easier to check results by hand calculations.
Although the deflected shape of the building gives some useful qualitative information and
often allows mistakes to be spotted, quantitative predictions of deflection with this type of
simple RC model cannot be trusted so no check on serviceability will be required.
LinPro Modelling
These tasks illustrate how one program output (here GSA) can be checked against another
(LinPro). LinPro is a very basic FE package that can only deal with 2D elastic moment-resisting
frames. You can think of it as a very primitive GSA. It is quite basic in terms of graphical
interface (and can be a bit buggy!) but the advantage is that a newcomer is less drowned into
thousands of functionalities that are only useful for experienced practitioners. Once you’ve
done this you’ll hopefully appreciate that all FE packages are based on a similar conceptual
skeleton (nodes, elements, materials, restraints, loads, analysis, and results). In terms of
structural behaviour, this section aims to explain why it is ok to use gross concrete crosssection
properties in a linear elastic FE analysis to calculate the internal forces.
Build a LinPro model of one of the two (identical) xz frames under wind load only (for
instance). Compare results to relevant GSA outputs. If you have made no mistake, the
results should agree within ~1% relative error.
Once your LinPro agrees with GSA, manually double the value of the concrete Young’s
modulus and rerun the model. Compare to previous bending moment and deflection
results obtained with LinPro (with real E). Explain what you observe.
Now calculate the uncracked second moments of area for the two types of members
including reinforcement (see separate handout). Update the LinPro model (original E)
with these new values of I and recalculate the internal forces. Compare previous
results and comment.
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Deliverables per group:
1. Report to the client (assumed to have some but limited understanding of structural
engineering)
Should include:
Brief intro
Assessment methodology: incl. your modelling assumptions, loading scenarios
considered, the rational basis for your capacity calculations. No generic waffle about
FEM or RC design or any other kind.
Summary table comparing calculated member capacities and critical design forces
obtained from GSA (specify the load case that cased it)
Conclude with final professional advice to client
Length constraints: up to 2 pages, up to two graphs, up to two tables.
2. Calculation Report – Should include:
Detailed hand-calculations of beam and column ultimate capacity
Hand calculation of the wind loads (wind pressure then wind point loads as input loads
in GSA)
Model Validation Checks:
o Hand calculations of column axial forces and vertical reactions due to dead
load only + comparison with GSA reactions
o Lower and upper bound hand calculation of shear and bending moments at the
ends of the longest beams under Load Combination 2 of the bending moments
at the ends and mid-span assuming (i) the end of the beams are pinned and
(2) the ends are fully clamped. Comparison with GSA output (should be in
between).
Checks against LinPro and structural behaviour understanding
Include comparison tables and comments as specified in the task section.
Format constraint: up to 6 pages, no GSA graphs allowed, only hand-drawn 2-D frames or
sketches should be included as necessary to explain calculations and results. Hand-written
calculations are fine. No appendix of any kind is allowed.
3. GSA Model file in soft copy
4. LinPro Model File (left with uncracked I values)
CEGE0009 GSA Assignment
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Table 1. Geometric and Material properties allocated to each group
Column Beam
Group No.
No. Storey
Storey Height (m)
No. Bay in X
Bay Length in X1 (m)
Bay Length in X2 (m)
No. Bay in Y
Bay Length in Y1 (m)
Width (mm)
Depth (mm)
Width (mm)
Depth (mm)
Concrete Strength
Class
Wind Speed (m/s)
Imposed Load
Category
*
1 3 3 2 6.0 4.5 1 3.5 400 400 300 250 C40/50 1.3 Restaurant
2 3 3 2 5.5 4.0 1 4.0 350 350 250 300 C35/45 1.4 Restaurant
3 3 3 2 5.0 3.5 1 4.5 300 300 200 350 C32/40 1.5 Restaurant
4 3 3 2 6.0 4.5 1 4.5 400 400 300 350 C30/37 1.3 Library
5 3 3 2 5.5 4.5 1 4.0 350 350 250 300 C25/30 1.4 Library
6 3 3 2 5.0 4.0 1 3.5 300 300 200 250 C30/37 1.5 Library
7 3 3 2 6.0 3.5 1 4.5 400 400 250 300 C30/34 1.3 Classroom
8 3 3 2 5.5 3.5 1 4.0 350 350 250 300 C32/40 1.4 Classroom
9 3 3 2 5.0 4.5 1 3.5 300 300 200 250 C35/45 1.5 Classroom
10 3 3 2 6.0 4.0 1 4.5 400 400 300 350 C40/50 1.3 Filing & Storage
11 3 3 2 5.5 4.0 1 4.0 350 350 250 300 C40/50 1.4 Filing & Storage
12 3 3 2 5.0 3.5 1 3.5 300 300 200 250 C25/30 1.5 Filing & Storage
13 3 3 2 6.0 4.5 1 4.5 400 400 300 350 C32/40 1.3 Dance Hall
14 3 3 2 5.5 4.0 1 4.0 350 350 300 350 C25/30 1.4 Dance Hall
15 3 3 2 5.0 3.5 1 3.5 300 300 250 300 C25/30 1.5 Dance Hall
* According to National Annex (NA) to BS EN 1991-1-1:2002
Assignment administration
Total weight: 15% of CEGE0009 final mark
Group formation:
This assignment in to be performed with your tutorial group.
CEGE0009 GSA Assignment
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Assessment criteria:
Report to client should be clear, professional and competent without being
overwhelmingly technical.
Calculation report should be clearly presented, well explained, well justified and
competent. FE results are sensibly checked and there is reasonably good agreement between
hand estimates and GSA values. Demonstrate good agreement and understanding in LinPro
section.
Weight breakdown:
Report to Client 25%
Calculation report 75%
Q&A Session 1 on Friday 8th Jan
Q&A Session 1 TBC
Submission Date: 12th Feb 2021 by 5pm.
Submission process:
Soft Copy Submission via Moodle Submission System (GSA Assignment Tab in CEGE0009
Moodle Page)
Upload one single zip folder per group. The folder should contain two separate files:
1. Reports (.docx or .pdf)
2. GSA Model (.gwb)
3. LinPro Model
Please make sure the name of the zip folder and all it contains includes your Group No. (NOT
student number or name).