PRESENTAION ON

LUSAS CIVIL AND STRUCTURAL SOFTWARE BY OLUKOTUN NATHANIEL .O. (96/O46621) CVE 656(COMPUTER APPLICATION IN CIVIL ENGINEERING)

LUSAS Civil & Structural is used throughout the world by engineers in the Construction Industry for all types of civil and structural design. It is available in three levels - Civil & Structural LT, Civil & Structural , and Civil & Structural Plus. 

It has a Windows User Interface, modelling wizards, comprehensive loading facilities, and Basic and Smart Combination facilities to provide for easy and rapid model generation, load application, and generation of results. 

ADVANTAGES

It reduces the amount of time you spend on analysis

It gives you a better understanding of the behaviour of your structure

It helps you to improve and optimise your design

The Windows User Interface, modelling wizards, comprehensive material libraries and Smart Combinations provide for easy and rapid model generation, load application, and generation of results.

The technology actively supports and encourages innovation helping engineers rise to the ever increasing challenge of aesthetic design and unusual structures.

The underlying finite element technology enables the true behaviour of structures to be accurately modelled for either global analyses of complete structures or local analyses of parts of structures such as a complex connection detail.

AREAS OF USUAGE

LUSAS tackles all types of structures, from

simple slabs, building frames, masts, towers

and tanks through to heavy civil

engineering structures such as cooling

towers, dams, docks and tunnels, It provides

a complete solution.

USES

For global analysis of all types of structures...

Simple / Complex Slabs Building frames Masts and Towers Grandstands / Stadia Storage Tanks / Silos Space Frame Roofs Cooling Towers Dams, Docks and Tunnels

For local analysis Plate girder buckling U-Frame action Local analysis of welds Solid modelling of box diaphragms Ultimate load analysis Fatigue analysis of structural

components

Case Study 1Spinnaker Tower

Tallest public viewing tower in the UK on completion

Concrete, steel and composite construction Category III check using LUSAS static,

dynamic and nonlinear analysis The Spinnaker Tower is a £35million, UK

Millennium Commission sponsored project aimed at transforming the waterfront of Portsmouth and Gosport. It forms the focal point of a £200M regeneration of the Portsmouth Harbour area and adds a new international landmark to the South Coast of Britain. 

Spinnaker Tower, PORTSMOUTH,UK

OVERVIEW

Tower Construction StagesSpinnaker Tower is a concrete, steel and composite structure that rises 170m from the sea adjacent to Gunwharf Quays. It has three tourist viewing platforms at heights of 100, 105 and 110m that offer extensive views over Portsmouth harbour and beyond. It is constructed upon a 3m thick pile cap and founded on 84 piles, and comprises two inclined slip-formed hexagonal concrete shafts, of 6m across, which merge into a single shaft at 70m. One shaft contains an internal express lift and the other shaft carries a panoramic external lift up the seaward face. 

MODELLING AND ANALYSIS

Static, nonlinear and dynamic analysis were all employed to analyse the model of the Spinnaker Tower in LUSAS. Ship impact, wind dynamics, wind-induced fatigue and the consideration of human perception of wind-induced movements at observation deck level all needed to be assessed in the design check. To do this, a model of thick beam and thick shell elements was created and used as a basis for the three distinct analyses that were carried out. In doing this the arbitrary section property calculator built into LUSAS was particularly helpful in deriving the section properties required for the varying cross sections of the concrete towers and of the steel bows, and helped to speed-up the building of the model

Load cases analysed included self-weight, dead loads, live loads, wind loads and various temperature differentials. Building services loads were generally applied as uniformly distributed loads, with major equipment applied as point loads. Wind tunnel testing provided the wind forces to apply to the model. Differential temperature loadings requiring detailed investigation included variations with respect to the assumed erection temperature, differing temperatures of each leg and for opposing faces of each leg, as well as differing internal and external temperatures for the mast and for the viewing areas. Long term creep and shrinkage was also investigated.

VIEWING PLATFORMS

The tower provides three high-level trapezoidal

viewing platforms that vary in size from 18m x 14m

down to 12m x 4.7m for the highest open deck. A grid

of I-section steel beams span between the concrete

tower, steel bows and frontal rib beams at each level to

support the 150mm thick concrete floor slabs. Each

platform was designed as a composite deck with

vertical vibration from crowd loading considered as part

of the design check.

CASE STUDY 2

DESIGN AND ANALYSIS OF ABOVE-GROUND FULL CONTAINMENT LNG STORAGE TANKS

Development of the world's largest ground LNG tank

Static, dynamic, thermal and nonlinear analysis

Strict design requirements met

LUSAS Civil & Structural software help develop and continually improve its range of above ground full containment Liquefied Natural Gas tanks.

LNG storage tank sizes of 140,000m3 were initially developed but now, using LUSAS Civil & Structural, an ground full containment LNG tank with a capacity of 200,000m3 was analysed and optimised.

ANALYSES UNDERTAKEN

In analysing and developing range of tanks, numerous finite element analyses were done with LUSAS including:

Static analysis Wind loading Modal and seismic analysis Temperature modelling Leakage modelling Pre-stress / post-tensioning Burn-out modelling Relief valve heat flux modelling Soil-structure interaction

STATIC ANALYSIS

For static analysis, 2D axis symmetric solid

element and 3D shell element models are built

and numerous static linear analysis load cases

are defined for various parts of the structure with

the roof, the walls, the base slab etc being

loaded independently. Load combinations then

allow the effects of the multiple load cases to be

assessed.

MODAL ANALYSIS

3D shell element modelling and eigen value analysis of the LNG tank outer shells and pressure relief platforms involves an examination of both the uncoupled and coupled response of the two structures. Lumped mass modelling is used for fluid/structure interaction of the LNG and for soil/structure interaction of the pile arrangements.

WIND LOAD MODELLING

3D shell element modelling is used to carry out wind load analysis of the LNG tank outer shell. For this analysis, half-models can often be used due symmetry of both tank geometry and loading. The wind load is varied around the circumference of the outer walls using a Fourier distribution providing a normal pressure on the forward face of the structure and a suction to the rear face.

SEISMIC ANALYSIS

Interactive Modal Dynamics techniques are used in the calculation of the dynamic seismic response. Operational Basis Earthquake (OBE) and Safe Shutdown Earthquake analysis assessments are also run to satisfy code requirements. The generated data from the structural analysis is integrated to obtain base shear forces and bending moments in the wall.

THERMAL MODELLING

For thermal modelling, 2D axisymmetric solid field and continuum elements are used and a semi-coupled steady state thermal analyses of LNG tank outer walls with insulation is performed. For this, an initial stress-free temperature is applied to all elements, and combinations of environmental conditions are considered for both the air and base temperatures. Results plots of hoop stresses in the top and bottom corners caused by a steady state thermal load are produced.

LEAKAGE MODELLING

Leakage modelling analysis investigates the effect of LNG spillage from the inner steel tank onto the Polyurethane Foam (PUF) insulation on the inside of the outer concrete tank at five different heights. The tank insulation is assumed to have been completely destroyed up to each level of the LNG under consideration. 2D axisymmetric solid field and continuum elements are used to model the tank outer walls and insulation down to the top of each leakage level. A semi-coupled steady state thermal analysis is carried out to assess the effects of the leakage

MODELLING PRE-STRESS TENSIONING

Large temporary openings in the wall mean that it is necessary to limit the effects of stress concentration caused by pre-stress forces. Loadings for each set of cables, both horizontally and vertically, are defined and assigned in separate load cases. These loadings can then be combined in different ways to achieve the required pre-stress sequence and/or loading pattern. Section slicing of the model is used to obtain axial forces and bending moments in the walls around the opening for selected load combinations.

BURN-OUT MODELLING

Modelling of a burn-out scenario involves 2D axisymmetric solid field elements and transient thermal analyses of the LNG tank outer walls. The tank roof and insulation layers (except any PUF layer), are assumed to have been destroyed, and are not included in the analysis. Steady state conditions are initially applied for a specified time. To model the burn-out situation, a temperature load of a specified peak temperature reducing to -170°C over a distance of 1.5m is moved down the inside of the tank at a constant speed for the burn-out time under consideration.

Relief valve heat flux modelling

With relief valve heat flux modelling, the tank bases are normally excluded from an analysis because they are considered to be remote from the heat flux loading. 3D solid field and continuum elements are used for a semi-coupled transient thermal analyses of a segment of an LNG tank. 

An initial stress-free temperature is applied to all elements and steady state conditions are established for an internal temperature of –170°C and a specified mean annual external temperature. A heat flux is then be applied to a specified region on the top of the roof for the number of time steps under consideration.

 

CONCLUSION AND RECCOMENDATION

From the results of the various LUSAS analyses it was shown that, despite its uniqueness and the use of different construction materials, the tower essentially behaves as a static/simple structure - results from the nonlinear models matched very closely the results from the slightly less well defined static model.

It can be deduced based on the case studies that LUSAS CIVIL AND STRUCTURAL Software is very efficient in structural analysis and design and therefore highly recommended for all types of civil and structural design.