Design of RCC and PSC Superstructures using LUSAS

Design of RCC and PSC Superstructures using LUSAS

  • Domain : CIVIL
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A Quick Overview

Packed with hands-on examples based on real structures and practical design techniques used in modern design offices, the course will equip students with all of the necessary skills to analyse, design and detail a concrete bridge superstructure. This course covers both reinforced and prestressed concrete. The focus is on superstructures which is everything from the bearings up. Most modern concrete bridge forms are covered, such as solid and voided slabs, ribbed decks, prestressed girders and box girders. The course also touches on steel-concrete composite design. Various analysis techniques are explained using hand calculations, struct and tie models and computer based FEA models with both grillage and shell elements. Advanced topics such as long-term effects, integral bridges and construction stage analyses are included. 


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COURSE SYLLABUS

1Concrete design refresher and bridge form selection

This lecture will introduce the course and the use of concrete as a construction material. Students are expected to have basic understanding of concrete design, but the lecture will remind them about the theory and key design principles. The lecture will also cover how concrete is used in bridges showcasing different forms and real-life examples where they are applied. It will explain where this material is most effective and tell how to choose appropriate form for a given site.

2Design of RCC solid Slabs

This lecture will build on concrete design basics by introducing the most basic form of concrete bridges – solid slab. The lecture will explain how moments and forces are distributed, introducing the principle of effective width. The students will learn how to analyse slabs using hand calculations, design aids (e.g. Pucher charts) and computer-based analysis. The lecture will cover bending and shear resistance calculations allowing students to derive a safe slab thickness and specify appropriate reinforcement. Other important considerations such as punching, deflection and cracking will be covered. As well as standalone slab bridges, the course will cover continuous multi-span slabs (e.g. transverse design of composite plate girder slabs) and cantilever slabs (e.g. box girder outriggers). The lecture will touch on design of skew slabs.

3Design of RCC voided slabs and introduction to grillage modelling

This lecture will develop from solid slab design introducing voided slabs. It will explain the analysis complexities introduced by inclusion of voids in the body of concrete and show how grillage modelling can be used to tackle them. Transverse distortional effects experienced by these types of cross section will also be covered. The students will learn how to design and detail voided slabs to tackle longitudinal bending and shear as well as transverse effects arising from distortion.

4Design of RCC ribbed slabs

This lecture will continue the theme of cast-in-situ bridges and will talk about ribbed slabs. It will go through further examples of grillage modelling and how it can be applied to analyse these types of bridges. Other methods of analysis, such as shell and beam type models will be demonstrated, explaining where this may be beneficial. The students will learn how to design a concrete T-sections, selecting appropriate effective width. They will also learn about interface shear between rib and slab. Various details will be discussed, e.g. where a cross beam is necessary and how ribbed slabs are constructed.

5Design of PSC I Girders

Students will learn about the benefits of prestressing compared to mild reinforcement. Various types of prestressing will be discussed, covering the differences between pre-tensioning and post-tensioning, and between bonded and unbonded tendons. Unlike reinforced concrete bridges, the prestressed bridges are often governed by serviceability limit state rather than ultimate capacity. The students will learn how to use stress-based calculation in order to check whether the structure is safe. The principle of brittle fracture will be introduced, demonstrating several real-life examples where this has led to catastrophic failure. The students will learn how to check whether the structure is no prone to brittle failure and how to prevent this type of behavior. This lecture will begin talking about long-term effects (creep, shrinkage and PT losses), priming the students for later course content.

6Design of PSC Box Girders

Building on the previous lecture, the students will learn how to design and detail concrete box girders. Various types of structures will be covered, from U-beam type bridges to straight and tapering multi-span bridges. The lecture will also touch on application of box girders in cable-supported bridges. The effects of torsion and curvature will be discussed. The students will learn how to analyse these types of structures and consider the aforementioned effects. This lecture will begin talking about construction stage analysis, priming the students for the later course content.

7Introduction to strut and tie analysis and local effects

The students will learn why beam theory is not always applicable in concrete bridge design. After listening to this lecture, they will know how to identify D (discontinuity) regions and draw appropriate strut and tie arrangement to capture their behavior. They will then learn how to resolve a strut and tie model by hand and using a truss type computer analysis. This lecture will explain how there can be different strut and tie arrangement for the same problem and why some are better than others, giving examples of typical real-life problems and their most efficient solutions. This lecture will also touch on local effects such as bottlenecking, splitting and multiaxial compression.

8Design of bridge details using S&T analysis

This lecture will continue the topic of struct and tie modelling and will dive into its application in bridge design. Classic bridge details will be shown, namely monolithic connections, half-joints, bearing regions, PT anchorages and stay-cable anchorages. Students will be demonstrated the advanced uses of strut and tie modelling and how it can be applied in 3D.

9Portal frame bridges and integral bridges

This lecture will talk about integral bridges, their advantages and limitations. Typical problems concerning integral bridges will be discussed, such as ratcheting behind abutment and the need for close collaboration with geotechnical engineers. Although soil-structure interaction is a large topic worthy of a separate course, its implications on design will be clearly explained. The students will learn how to design a basic portal frame bridge and how to detail the abutments of a longer span concrete bridge.

 

10Composite plate girders and trusses

This lecture will focus on application of concrete in composite bridges. The student will apply skills of grillage analysis and slab design which was acquired earlier and apply them to composite structures. They will learn how to calculate elastic and plastic section properties using effective Young's modulus method. They will be demonstrated how to perform basic structural checks of a composite plate girder and truss bridges including design of shear studs. 

11Long terms effects

This lecture will focus on the long-terms effects, namely creep, shrinkage and loss of prestress, which had been introduced earlier in the lecture series. They will learn how to calculate long-term section properties. Examples where creep and shrinkage cause parasitic effects will be demonstrated, e.g. moments in continuous prestressed bridges and composite girders.

This part will also discuss the movement ranges and calculations related to the expansion joint specification. Movement and friction at bearings will also be mentioned.

12Construction Stage Analysis

This lecture will demonstrate various ways in which concrete structures can be constructed, e.g. cast-in-situ, launching and balanced cantilever construction. The students will learn that construction sequence can often govern design and that structures should always be checked in their temporary conditions.


Projects Overview

Concept design for a concrete viaduct in a river flood plane

Highlights

Key Highlights:

  • A real site will be given as a starting point with some relevant constraints, such as preferred alignment, head clearances and obstacles.
  • Based on bridge forms covered in weeks 1-6 create a concept design stating span arrangement and construction depth.
  • Sketch out a solution giving major dimension and a cross section.
  • Create a model in Lusas to analyse the forces going through the structure.
  • Design major structural elements to carry the forces using calculation methods demonstrated in the lectures.

Deliverables:

  • Sketch showing span arrangement, support positions, key features and dimensions.
  • A note explaining the reasoning behind the design decisions.
  • Sketch showing a typical cross section.
  • Sketch showing reinforcement layout and quantities.
  • Valid analysis model with all of the major load cases included.
  • Hand-written or excel based calculations demonstrating that the bridge is adequate.
  • Excel table of quantities.

Detailed assessment of a major new bridge scheme across a congested industrial site

Highlights

Key Highlights:

  • A concept design for a multi-span concrete bridge will be presented in a form of a sketches.
  • The design will incorporate elements from all 12 weeks including steel-concrete composite spans and integral spans.
  • The task is to create a detailed analysis model and a set of calculations covering everything from stability checks to serviceability criteria (e.g. movement at joints).
  • The design must include a safe way of construction and analysis proving that the design is adequate at all stages.
  • The exercise will require design of smaller parts and D-regions as well as major elements.

Deliverables:

  • Elements sizes for major elements and highlighted details.
  • Detailed analysis model including staged construction and time-dependent effects as well as all of the effects covered in Project 1.
  • A set of calculations demonstrating adequacy of the members and compliance with design criteria.
  • Sketches showing all major reinforcement and quantities.
  • Excel schedule of quantities.