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日期:2021-02-12 11:45

CEGE0009 GSA Assignment

Dec 2020 Page 1 of 6

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

Dec 2020 Page 2 of 6

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 fa?ade nodes and the magnitude of each load will be calculated by hand

CEGE0009 GSA Assignment

Dec 2020 Page 3 of 6

assuming that each node takes the resultant of the pressure on the tributary area of the fa?ade

(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.

CEGE0009 GSA Assignment

Dec 2020 Page 4 of 6

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

Dec 2020 Page 5 of 6

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

Dec 2020 Page 6 of 6

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).


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