Auto Cad And STAAD Pro

This chapter gives an insight into the topics involved in this dissertation, it starts with a review of the key items involved to complete this project such as the programs used to design and analyze the structure as in Auto cad, and STAAD pro. The chapter further develops in reviewing the euro codes in which the building will be designed to.

Auto Cad

This is a design and documentation software program that was founded in 1982, 28years ago. It is the most commonly used piece of software of its kind and it is constantly being enhanced and improving its software to meet the current needs of its users.

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It is used for drawing objects to a very high degree of precision in either 2D or 3D format using polar coordinates. Almost any object conceivable like the 3D model shown in figure 2.7 can be produced on today’s Auto cad thanks to its extensive array of tools and when trained, easy to use interface.

Its tool base may be used in both the 2D and 3D formats, some of the basic tools include, line, circle, arc, break, extend, mirror and copy. These are only a small fraction of the features of Auto cad, which make it possible to create and change or redesign models of any shape and complexity, in a relatively short period of time as compared to drawing by hand or using other software programs such as STAAD pro.

This is the reason why auto cad was used to detail the design rather than STAAD pro because of its ease of use and the complexity of the design and then inputted into the STAAD pro software for the analysis.

STAAD Pro

This is a finite element analysis and design software program run on windows operating systems, which is used to analyse the structural stability of structures, under a variety of conditions. It allows the users to effectively analyse structures built from a number of different materials such as, timber, concrete, aluminium and steel, under different forces caused by, earthquake, soil interaction, and various dead loads and live loads, which are specified by the local design codes being used in whatever location the structure is being design, in this case Eurocodes.

It is a very versatile piece of software that has being perfected over the past 25 years, it reduces the amount of man hours required to correctly analyse how a structure will behave when loaded using either 2D/3D model generation. The general steps involved in producing a successful model are as follows:

Model generation: – creating the structure model in either 2D or 3D which could involve importing an Auto Cad files and then choosing the material type and size for the members, applying a foundation types to correct locations and specifying loads and forces on the model.

Calculations:-to obtain the analytical results.

Code check:- creating parameters for design specification

Running analysis:-to perform analysis and design.

Verification of results:-displayed through graphs, diagrams and tables.

Reporting and printing.

Eurocodes:

This chapter is intended to provide a brief introduction into the eurocodes. It will list the benefits, the problems, associated with the codes. It describes the general layout of the codes and discusses the difficulties with the drafting of the codes and how the difficulties were resolved, the national annex and their roles will also be discussed.

It will advance to describe in detail to list the difference between the previous BS 8110 and the contents of Part 1.1 of Eurocode 2, which has superseded the above British standard. And will be the main eurocode used to design this concrete structure.

The eurocodes are set of ten codes of practice for the design of building and civil engineering structures in concrete, steel, timber, masonry & other building materials Table 2.1 lists these eurocode there titles and reference numbers. Similar to the previous codes of practice the British standards these codes come in a number of different parts, each containing different rules to the design of the different structures included in the codes.

Table 2.1

EN1991 provides the characteristic values of the loads or actions as termed in the code, needed for the design. It is the head code of the world fist material independent design code providing guidance on determining the design value of actions and combination of actions, including partial safety factors for the actions. EN 1997 covers the foundation design with respect to the geotechnical side. EN1998 is devoted to the seismic design and provides guidance on achieving earthquake resistance in buildings and structures.

These Eurocodes will have the same legal standing as the previous British standards and other approved documents. These codes were published first as preliminary standards; know as ENV (Norme Vornorme Europeenne), in the beginning of 1992. Now after being revised & reissued as European standards, known as EN (Norme Europeenne), along with national annex which contains supplementary information, are coinciding with British standards but will eventually become mandatory and all conflicting standards will be withdrawn as in the British standards.

Benefits of Eurocodes.

There are many advantages of having design standards which are accepted by all member states how ever this is not a new initiative as the first draft Eurocode 2 for concrete structures was based on the CEB (Comite Europeen du Beton) Model Code of 1978 produced by a number of experts from various European countries, similarly Eurocode 3 was based on the 1977 Recommendations for design of steel structures published by ECCS (European Conventional for Constructional Steelwork). The original reason for this work was to improve the science of structural design. Recently though the drive is for political and economic unification of countries and these Eurocodes will help to lower the trade restrictions and barriers which exist between member states and allow for contractors and consultants to compete freely and fairly for work within Europe. Also the unification will enable products, materials, components, design programs to be marketed throughout member states. It will also improve international standing of European engineers which should help in increasing their chances of wining work abroad.

Prooduction of Eurocodes:

Each Eurocode has been drafted by a team of experts from different member states. These groups are under contract to the CEN (Comite Europeen de Normalisation), the European standards organisation, whose members are the national standards bodies as in the British Standards Institute in the UK. During the ENV stage of production a liaision engineer from each member state was involved in evaluating the final document and discussing with the drafting team the acceptability of the eurocode in relation to the previous national code.

Format of Codes:

Problems associated with drafting the Eurocodes.

There were many problems faced when the Eurocodes were being drafted mainly being the terminology that was to be used, different climate conditions, materials and different work practices from the different member states. The following details outline ways in which these problems were overcome.

Terminology

From the beginning it was inevitable that the terminology would have to be standardised in general the agreed terminology was found to be similar to that used in the UK national standards. The few minor differences include loads are now called actions while dead loads & live loads are now referred to as permanent and variable actions respectively. Similarly bending moments & axial loads are now called internal moments and internal forces respectively.

Principles & Application Rules

This was the method used to divide the documents into sections ensuring documents were concise, described the overall aims of the design & provided specific guidance as to how these aims can be achieved in practice.

Principles comprise of general statements, definitions, requirements and models for which no alteration is allowed.

Application Rules are generally recognised rules which follow the statements & satisfy the requirements given in the principles.

When the letter P is missing from the clause number it indicates an application rule. The use of alternate rules other than that in the eurocodes is permitted as long as hey do not effect the design requirements and are at least equivalent to those suggested.

National Annexes

Differences in work practices, climate conditions etc required the allowance for different parameters to be determined and specified at a national level such as safety factors, cover particular methods of construction etc. where these deviations are allowed a note in the code is provided in the accompanying annex, these parameters are know as NDPs (Nationally Determined Parameters).

Eurocodes 2: Design of concrete structures.

This will be the main Eurocode used to design this structure as the build will be mainly concrete this code is to replace the previous code of practice BS8110 and it is the European standard for the design of buildings in concrete, although the ultimate aim of Eurocode 2 and BS 8110 is largely the same to provide guidance on the design of buildings and civil engineering works in concrete, there are many new design procedures and differences, it is based on a limit state principles and comes in four parts as shown below in table 2.3

Liquid retaining & containment structures

Part 1.1 of Eurocode 2gives a general basis for design of structures and some detailing rules very similar to the previous BS8110, the design cannot not be completed without using reference to other documents such as EN 1990 (Eurocode 0) and Eurocode 1 to determine design values of actions (loads), Part 1.2 of Eurocode 2 for fire design, EN 206 for durability design & Eurocode 7 for foundation design. The reason for this difference in structure and layout is to make the eurocodes more concise than BS 8110 and avoid repetition.

Proposed Design:

In the design process a number of different designs were considered and working with the requirements of the structure the most suitable one was chosen these requirements were as follows:

Design a suitable multi-storey building containing retail units and accommodation units. The structure should be designed and built to modern codes of practice and standards. The building must be of modern aesthetics and be unique to surrounding buildings. Also the structure should fit the following criteria:

Retail Floor Space ; between 1500 & 4000m2

Accommodation Space ; between 10000 & 30000m2

Maximum Footprint ; between 1500 & 3500m2

Maximum Height of Building; 40m.

The following designs were considered and compared when choosing the final design.

Proposal One;

Retail space = 3161m2

Accommodation space = 11718m2

Footprint = 3161m2

Provision for lateral stability and vertically stability is provided by concrete columns and shear walls/shear cores within the structure.

Proposal Two;

Retail space = 2001m2

Accommodation space = 11674m2

Footprint = 2001m2

Provision for lateral stability and vertically stability is provided by concrete columns and shear walls/shear cores within the structure.

Proposal Three;

Retail space = 1558m2

Accommodation space = 28451m2

Footprint = 1558m2

Provision for lateral stability and vertically stability is provided by concrete columns and shear walls/shear cores within the structure.

Chosen design:

The design in proposal two was chosen finally because when it was compared with the other designs it was decided that it was more astethic than proposal three because of its falling design, it was then compared with design one and it was not considered to be more asthetic but it did accomodate the footprint requirments and space requirments better than proposal one did.

Materials & Methods:

Elevator & Elevator Shaft; The elevator shaft will provide latheral stability for the building and will direct forces into the ground, it will span from the base to the roof in each of the four shafts. There will be four elevator shafts positioned in the centre of each external face of the building, providing ease of acess to each floor. Each one will be of dimensions 3 x 2m and will utilise a electric cable borne method for lifting and will travel at a max speed of 2.5m/s. Each elevator will be able to accomondate a max of 10 peolple at a time.

Latheral Stability:

The elevator shafts incorporadted in this design provide for latheral stability caused by wind loads, these loads are created by the wind force on acting on the external face of the building transmiting the loads to the floor, these floors form horizontal diaghragms transfering the latheral load to the vertical rigid elevator shaft which acts as a vertical cantillever and subsequently transfers the loads to the foundations. The advantage of using the elevator shaft to provide lateral stability is that concrete walls tend to be thiner than other bracing systems used in medium sized multistorey construction and so save space in congested areas also they are very rigid and may be used as fire compartment walls, the disadvantge of using the elevator shaft for latheral stability is that construction is slower and less accurate and when constructed they are not easily modified, also it is difficult to provide connection between steel and concrete.

Procedure – STAAD Pro

1.1 Importing drawing

Now that both the model had being created and the loads calculated, it was now time for the analysis of the model. To achieve this, first the model had to be imported into STAAD pro, this was done by saving the model in Auto cad as a R12/LT2 DXF file, which is compatible with STAAD pro, and then opening a new structure sheet in STAAD pro and using the import function located in the file drop down menu. When importing the file the following two pop up windows will appear shown in figure1.1 and figure 1.2, these let you define the orientation and units you want to analyse your model in. For the structure model meters and kilo Newton were chosen with a standard orientation of the Y axis pointing upward.

After that the model will appear on the main STAAD Pro interface as shown in figure 1.3. As can be seen from figure 1.3, STAAD Pro has a vast array of tools and functions that make it possible not only to, analyse almost any structure in almost any situation, but also to draw structures. For simple structures it would be worth while using STAAD Pro, however for more complicated structures it is better to use Auto cad, because it is specifically tailored for drawing almost any structure or object with ease, for the trained user.

Now that the model was now in STAAD pro, it was now time to proceed with further developing the model for analysis. On the left hand side of the main window containing the model, there is a tool bar called modelling, this toolbar contains functions for modifying the model, like design, support, general, load, material etc.

1.2 Adding supports

For the model, supports were required at every base node position. To achieve this, the support window was selected from the general toolbar, figure 7.5 shows the window that pops up for adding support to your structure. For this model fiixed support was required so the create button was selected, and fixed support in the sub menu was chosen as shown in figure 1.4. Now that the option for fixed support was now in our main support window, it was now time to apply the support. STAAD pro gives you a number of different options of assigning the support, like, assign to view, use cursor to assign and assign to edit list, and assign to select nodes.

First the node function was selected from the cursor toolbar as shown in figure 1.6, this option allows you only to selected nodes and not beams. When this was done, the bottom layer of nodes on the model, were select and the assign to selected nodes function was used. Now fixed support were applied to the model in the correct position as shown in figure 1.7, and it was time to proceed with the next step.

7.3 Member selection

From the general toolbar, the properties window was selected. From here you can assign any style of member in accordance with many different regions building codes using the section database function, and apply any number of different sections to different members in the same model. You may also design the dimensions as in this case a 300mm by 280mm rectangular concrete section was chosen for the beam and a 300mm by 300mm concrete section for the column was detailed. Once selected, the section chosen appears in the properties window, and from here you are given the same option as applying support i.e. (assign to view, use cursor to assign and assign to edit list, and assign to select beams).

First the beam function from the cursor toolbar was chosen, this allows you to only select beams and not nodes. Then the columns were assigned using the same process with the different section assigned, figure 1.9 shows the model with the beams and columns applied.

Now that this was completed it was now time to move on to applying the various loads to the model.

7.4 Applying loads

Loads are used to estimate how a structure will behave if constructed. Since the loads had being previous calculated with the aid of eourcodes, it was now possible to apply them to the structure.

In the general toolbar, the load window was selected, from here all types of load may be applied to the structure, for the dome the loads calculated were, dead load, live load, and wind load. From the load window, the load cases icon was selected, a pop up window as shown in figure 1.10 was activated.

From here all the three types of loads were identified and added to the main load window. Each load name was then picked individually by used of a pop up window known as load items which is shown in figure 1.11 and the specific load applied.

Now that the loads had being picked and values assigned to them in the appropriate direction, it was now time to apply the loads to the model. In the load window the same options exist as for the support and properties window for applying items to the model, for the dead and imposed load, the assign to view function was used. For the wind load only the side facing the wind is loaded, so the node cursor was selected from the cursor toolbar and all the nodes on wind facing side of the structure was selected as shown in figure 1.12.

7.5 Running analyse

First the analysis/print toolbar was selected from the modelling menu, which resulted in two windows being activated, the print analysis commands window and analysis – whole structure window, which are shown in figure 1.13.

In the analysis commands window the no print option was selected and added to the analysis – whole structure window, which shows the processes involved in the analysis. After this was completed the analyse toolbar located at the top of the user face was selected, and the run analyse option selected as shown circled in red in figure 1.14.

After the analysis in completed a window the STAAD analysis and design window shows the processes carried out and whether there are any errors or warnings related to the model. Any problems relating to the model may be checked by selecting the errors or warning in the window, and the exact problems with the members they are related to, will be displayed. Figure 7.15, shows the final analysis of the dome model which took 16 seconds with no errors or warnings, after all the errors and warnings were corrected.

7.6 Post processing

On the bottom left of the STAAD analysis and design window, there is a set of options on where to go after the analysis, the go to Post Processing Mode option was selected and done button pressed.

Form here, the post processing window as shown in figure 7.16 the results of the analysis may be viewed for both the beams and the nodes. Graphs and reaction tables along with visual representation can be viewed for the nodes, showing things like the max displacement of a node. Stresses, graphs and forces can be viewed for beams showing such things as max axial forces, max bending, max shear and max stresses.

7.7 Producing reports

The number of results including structure type, No. of nodes, No of members etc can be put into a report format. This is a useful tool for an engineer to document any findings to produce to clients or planners, an example of a node report for the dome is shown in figure 1.17.