Case Study Cable stayed bridge over the River Labe at Nymburk Design and construction of a longitudinally prestressed extradosed bridge Detailed 3D modelling to analyse live load effects on the structure Good correlation obtained with static and dynamic load tests Pontex Consulting Engineers Ltd. used LUSAS Bridge to assist with its design of a slim, cable stayed bridge on behalf of the Roads and Motorways Directorate of the Czech Republic. The bridge incorporates a number of original structural elements and technologies, and provides a modern, light, and aesthetically pleasing solution to crossing the River Labe. The bridge is the first cable-stayed bridge in the Czech Republic with two planes of stays and low pylons, characteristic of an extradosed type of cable stayed bridge. Overview Located to the north-east of Nymburk in the Czech Republic, and situated in the flat plain of the Labe lowlands, the bridge carries the I/38 road over the River Labe as part of a by-pass scheme built to alleviate traffic congestion from the historical centre of the city. Due to the requirements of the Labe Basin Authority, a main span of 132m together with a very shallow structural depth for the bridge superstructure was required. As a result, a so-called "extradosed“ main bridge structure with low pylons was developed, representing a transition between the traditional cable-stayed bridge and a bridge with external prestressing tendons. Elevation Bridge design The complete bridge crossing has a continuous superstructure 530m long with expansion joints located only at the abutments. The main concrete bridge superstructure consists of a 132m span over the River Labe and two adjacent 41m spans that are directly connected to the approach spans.The concrete deck sections of the main span are of a symmetrical double-girder shape of variable depth and width, and are supported by sets of 3 parallel grouped stays anchored to the 16m high pylons. The middle section of the main span was designed as a relatively lightweight composite steel-concrete drop-in structure. This 52m span comprises two main steel box girders that are tied by steel I section cross beams at 3.0m centres. The thickness of the lower and upper flanges and webs of the main steel girders vary in accordance with the magnitude of the internal forces. After being delivered to site by barges the box girders were lifted into place and welded to 700mm long steel members that were cast into the concrete structure and tied to it using longitudinal prestressing anchors fixed to the end plates. Shear studs tie a 245mm thick reinforced concrete slab to the steel girder structures. Pylons The 16m high, heavily reinforced concrete pylons are topped with hollow steel plated box chambers for anchoring the cable stays. The anchor plates are one of the most highly stressed parts of the structure and were fabricated from 150mm thick steel plate. Welded into the front face of each anchor plate are six, 377mm diameter, 16mm thick steel tubes through which the stays were passed and then anchored. The bottom flange of the chamber is formed from 50mm thick steel plate with stiffeners to provide a uniform distribution of the forces to the concrete section. The side walls of the box are of 40mm thick plate with 50mm thick vertical stiffeners at the anchor plate locations. Steel studs, welded uniformly to the sides and top of the box chamber, bond the steel box to the self-compacting concrete that was subsequently applied. A 600mm square manhole cover in the top of the pylon provides maintenance access. Cross beams and rocking struts At the pylon locations the bridge deck has massive cross beams which help to distribute the loading from the longitudinal girders and pylons to the bridge bearings. Prestressed anchor cross beams are also used where the cable stays are anchored to the bridge superstructure. Piers, located where the back hangers of the bridge are anchored, are designed as rocking struts in order to be able to resist both tensile and compressive forces and to allow for expansion of the structure. The rocking struts are made of 610mm external diameter seamless steel tubes. At both ends of the strut an accurate four-shear pin joint is formed. The pin joint anchor plates are attached to the bridge deck and elements of the bridge substructure using prestressing bars. Modelling in LUSAS A detailed 3D model of the complete bridge structure including the approach viaducts was created in LUSAS. Solid hexahedral elements modelled the concrete deck and pylons. Thick shell elements modelled the steel members of drop-in span and pylon anchorage boxes. A separate 3D solid element model of a pylon box assembly was also created to investigate the localised stresses in this highly stressed part of the structure. Eigenvalue analysis obtained the first 15 mode shapes and gave a good indication of the potential response of the structure. A static analysis investigated the effect of live loads in the transverse direction, and also investigated the effects of any eccentric position of live load on the longitudinal forces induced in the deck and cable stays. Because deck displacement due to off-centre vehicle loading was of interest to Pontex a number of displacement plots were produced showing displacements caused by a variety of applied loads and load combinations. After completion of the bridge both static and dynamic load tests were carried out showing very good correlation with the LUSAS predicted results, effectively verifying the modelling approach used. Now open The bridge opened to traffic in May 2007. Pontex Consulting Engineers Ltd., believe that because of its location, and by the introduction and use of a number of original structural elements and technologies, the bridge will help contribute to the further development and use of modern light cable-stayed structures in the region and, in turn, become one of the most outstanding bridge structures in the Czech Republic. "By using LUSAS on this project we obtained an accurate assessment of the deck displacements caused by the static and dead loads. The easy-to-use modelling capabilities and the re-use of previously defined load patterns helped enormously with this." Václav Kvasnička, Consulting Engineer, Pontex Consulting Engineers Ltd. Main parties involved in this project: Client: Roads and Motorways Directorate of the Czech Republic – Prague branch Designer: PONTEX Consulting Engineers Ltd. Main Contractor: Joint Venture SMP CZ, a.s. + Metrostav, a.s., D.4 + PSVS, a.s. Contractor for the main bridge: SMP CZ, a.s. Contractor for the approach bridges: Metrostav, a.s., D.4, together with Sub-contractor JHP mosty, s.r.o. Subcontractor for the steel work: MCE Slaný, s.r.o. This case study was created with reference to a technical paper presented by Milan Kalny of PONTEX Consulting Engineers Ltd. at the IABSE Symposium on ‘Improving Infrastructure Bringing People Closer Worldwide’, Weimar, Germany, 17-21 September 2007.

Case Study
Analysis and Design of Avenues Walk Flyover

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Detailed 3D analysis of one of the longest and most highly curved single span girder bridges in the world
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Investigation of lower lateral bracing requirements
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Uplift analysis for deck pour sequence

Avenues Walk Flyover

Avenues Walk Flyover is a single-span curved girder bridge that spans the Florida East Coast Railroad to provide access to a private mixed use development on a restricted site south of Jacksonville. GAI Consultants used LUSAS Bridge analysis software for detailed 3D analysis and comparison checking of the structure, and notably to investigate lower lateral bracing options and to provide a means of reducing uplift during a slab pour construction sequence.

Overview

Avenues Walk Flyover provides access to a triangular-shape mixed-use development site bounded on two sides by Interstate 95 and the Florida East Coast Railroad.

Site (red outline) accessed by Avenues Walk FlyoverThe bridge alignment was essentially dictated by the grade required for the access road to rise sufficiently within the land space available in order to meet a specified railroad clearance. The severe curvature and length of the resulting bridge required the development of innovative design and construction methods to meet both geometric and economic restraints. GAI’s eventual solution, with a span length of 218’, a width of 79’ and a centerline radius of 300’, means that Avenues Walk Flyover is one of the longest and most highly curved single span girder bridge structures in the world.

To achieve the combination of span and curvature for this bridge required unique design elements in order to optimize capacity and ensure stability. Varying end skews, non-uniform girder spacings and girder depths, lower lateral girder bracing, uplift resistant bearings, a 32 ton concrete counterweight, and a transversely staged deck pour would all end up being incorporated into the final design.

Initial and re-designed bridge alignments and final single deck solution

Bridge development

Concept designs looked at a single-span and a three-span option, with the lower cost single-span option being preferred by the developer. For this, separate 37’ wide, single-span eastbound and westbound structures were initially proposed but the potential for uplift on these separate, narrow, and highly curved structures resulted in one single 73’ wide structure of greater stability being chosen. Further investigations into different skew arrangements and relative stability/uplift issues for this wider structure resulted in a final solution which used parallel end supports, one radial with some potential for uplift, and the other skewed to the roadway at about 45 degrees. To support the deck, eight centrally placed, equally spaced girders were proposed, but from analysis carried out it was found that, because of the severe curvature of the deck, the two girders on the outside edge were carrying four to five times more moment than the innermost girder. This caused GAI to move the set of girders more toward the outside of the curve, reducing the deck overhang. This gave a beneficial 10 percent reduction in load distribution for the most heavily loaded girder. Girder spacing was also adjusted. Spacing for the two outer, 120” deep girders was decreased from a fixed 9’-5” to 8’-0”, and the five inner, 104” deep, girder spacings were increased to 10’-0”. The 300’ centerline radius on the bridge required a 4% superelevation, making the outside curb line almost 34 inches higher than the inside curb line. Because of this, the outside girders, which are only 16” deeper than the inside girders, do not control the under-clearance, so by using shallower girders for the inner six locations, ten valuable inches of overall bridge height were saved.

Avenues Walk Flyover showing falsework towers

Analysis and design

In order to verify the bridge’s behaviour during both erection and in-service loading both grid and finite element analysis software was used. 2D grid analysis was employed essentially as a ‘framework’ tool for overall girder design, flange plate optimization, diaphragm design, and bearing design. 3D finite element analysis with LUSAS Bridge was used for detailed design to make sure that 3D effects were being accounted for in the individual bridge elements - something not possible with a grid analysis. Using LUSAS, dead load effects were assessed and final construction deflections were derived. Live loading was analysed for each vehicle lane with combinations and envelopes producing worst-case values. LUSAS was also used investigate bearing stiffnesses, lower lateral bracing loading, and to assess potential uplift from transverse deck pour sequences. A final analysis of the complete proposed design was carried out by a third party to verify the results obtained.
LUSAS 3D modelling of Avenues Walk Flyover showing vehicle loading to inner lane

LUSAS 3D modelling of Avenues Walk Flyover showing vehicle loading to inner lane



Lower lateral bracing to the two outer girdersLower lateral bracing

Using LUSAS Bridge, GAI investigated lower lateral bracing options to carry wind and lateral stresses in the plane of the girder bottom flange. Three arrangements were examined; lateral bracing in both exterior bays and one internal bay, lateral bracing in the exterior bays only, and lateral bracing in the outside girder bay only. Based on some preliminary analysis, it was determined that final condition lateral deflections and stresses were not large enough in the innermost girders to warrant the cost of installing lateral bracing in that bay. In the erection condition, however, the use of lower lateral bracing would have had an impact on the magnitude of lateral deflection if the interior girders were erected first. Since the planned construction sequence was to erect the outside girder pair first, the potential advantage of lateral bracing would not, in fact, be realized. The final design included a single bay of lower lateral bracing, placed between the two outermost girders.

Deck pour sequence analysis

The steel frame was erected on two falsework towers. However, prior to the deck placement, the towers were removed. As a result, uplift, calculated to be caused by pouring the deck, had to be overcome. With the entire steel frame in place to resist the effects of overturning, a concrete counterweight weighing 32 tons was placed adjacent to the inside edge girder at the radial abutment to reduce any uplift forces. Additionally the deck was placed in two transverse deck sections with the deck over the four innermost girder lines placed first. After the deck cured, the remaining section of the deck was placed, with the first pour acting as a counterweight. The bridge was constructed using uplift resistant bearings and uplift resistant foundations at the inside edge of the radial abutment so that there was adequate capacity for the entire uplift including live load effects shown in the worst-case analysis model.

From analyses, mid-span dead load deflections were calculated and compared for each girder. After the removal of the falsework towers the calculated deflection for the outermost girder varied from 10.8 inches in the LUSAS 3D finite element model to 13.4 inches in the 2D grid analysis model, a variation of about 25 percent. This difference would be largely due to the limitations of grid analysis to include lateral bracing effects. The models showed good agreement regarding the end reactions and the uplift potential at the radial abutment. For the maximum downward reaction case at the outermost girder the models all agreed within 2 percent.

Samuel N. Spear, engineer at GAI Consultants said: “LUSAS proved to be a valuable tool for the project. We especially enjoyed the ability to model the various stages of construction and in-service loading. He was also complimentary of the LUSAS support staff: “When we required modelling assistance the LUSAS support staff were helpful in answering our questions when the need arose”.

Avenues Walk Flyover Project Stakeholders

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Owner: City of Jacksonville, Florida
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Engineer: GAI Consultants, Inc.
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Contractor: Hal Jones, Inc.
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Railroad: Florida East Coast RR
* Developer: KIMCO Developers, Inc.



“LUSAS proved to be a valuable tool for the project. We especially enjoyed the ability to model the various stages of construction and in-service loading."

Samuel N. Spear, GAI Consultants

Financial Crisis

Hi all,

I have one issue to discuss...

Well, As we all know about the financial meltdown across the Globe leaving the finance giants and banking sectors in a HUGE HUGE trouble.

Most of the construction companies and infrastructure developers are indirectly affected from this Financial Meltdown, since they get their finances for the project from these finance and bank sectors....

So now the issue is:

“What can we (Infrastructure Developer/Government) do to come out of this FINANCIAL DEPRESSION?”

Putting in simpler terms what strategies can be thought of, so as to ease the fund flow?

To minimize the effect our Finance Minister has come up with a strategy to lower the Interest Rate and try to boost the present financial condition...[Source: Business Line]

What can be the other mechanisms to avoid/minimize the effect of Financial Crisis?

I know that this problem is not so easy to solve...

One option would be to give a pause to the development/improvement programs for the time being!

Another option would be to take small projects, which involves lesser capital and can be borne by the developer himself.

Another (Strange & Out of Hat) option would be to do every development/improvement project on CREDIT!!!

Can you suggest some of the strategies??? Since the thoughts what I mentioned above are not the right solutions!!!

land acquisition procedure

land acquisition procedure

Hi everybody
This is Vineet Deshmukh. As we had discussed in class, land acquisition is often the single most important risk in private financed transportation infrastructure. To emphasis how cumbersome the process is, I thought of sharing with you all the procedure for land acquisition as per the National Highways Act. the different steps of land acquisition are described in the different sections of the act, as follows:

3A(1) Notification in official gazette

3A(3) Notification in 2 local newspapers, 1 of which will be in vernacular language

3B Obtaining power to enter land for survey


3C Hearing of objections

3D Final & binding declaration of acquisition by notification in official gazette {has to be done within 1 year of 3A(1) excluding period of court injunctions}

3E Take possession within 60 days of service of notice

3F Right to enter land and do any act

3G Determination of amount payable as compensation after giving notice in 2 newspaper, inviting claims of persons with interest and resolving disputes if any through arbitration

3H Deposit of money to person entitled



So now you know why more often than not, our infrastructure projects are behind schedule.......

PPPs in US infrastructure

PPPs in US infrastructure

This months issue of the Journal of Construction Engineering and Management brought out by the American Society of Civil Engineers has an interesting article on the use of Public Private Partnerships (PPP) in US infrastructure projects.

As we all know, most infrastructure in the US is quite old and is in great need of renewal and replacement. PPP is an efficient way of mobilizing resources and achieving optimal project performance. So how many of the infrastructure projects in the US are done through the PPP mode?

The authors conduct a survey and find out that only 12% of the organizations surveyed have used BOTs or PPPs to build infrastructure!! The authors then attempt to understand why the other 88% continue to use conventional modes of public finance and come up with several explanations. A common thread that runs through these explanations is a lack of capacity within public agencies and a lack of exposure to PPP's, thereby making the implementing agencies a little skeptical of the overall potential of PPPs. In addition, the US also has no laws on PPPs unlike the Model Concession Agreements in India.

The research done in this paper is not very rigorous - the method of analysis is merely a straight aggregation and averaging of survey data. However, what is interesting is that the lack of capacity (i.e. understanding, know-how of fundamentals) as regards PPP leads to an over-reliance on public procurement even in developed countries. Many of the same arguments explain why there is a lot of rhetoric on PPPs in India, but relatively few projects that are actually implemented in this fashion.

What can we do to improve the situation? Comments?

multi cultural projects

multi cultural projects

hi all,
There's an interesting article about the risks faced in a multi-cultural venture in an infratructural project. There has been a rise of multicultural project teams, widely separated by geography with team members from different cultures and backgrounds working together to achieve a common objective, in past few years. The key factors affect the success of these projects can be as follows:

• The lack of physical proximity is the first key factor. The geographical separation of a project team poses difficulties of communication.
• For the project manager of a multicultural project, there can be difficulties in assessing the skills and competencies of team players. Training and education standards and the relative value of qualifications can be very different in different parts of the world. Job methods vary and can be different because of specific local conditions such as working in heat, earthquake risk or local trade practices.
• Mobility can be a problem that affects competence: it can be difficult to find people who can work effectively away from their home environment.
• Another key issue affecting multicultural project teams is language. A project must have a common language to ensure a common understanding. In many situations, this means that non-native speakers are working in their second or third language with a consequential loss of effectiveness, as well as increased risk of mistakes or misunderstanding. In situations where interpreters or translators are required, this has the effect of significantly slowing down the whole communication process and is very costly. Even where team members of different nationalities speak the same language, there can be difficulties. Words in American English can have totally different meanings to English in the UK, whilst conventions and abbreviations can often be very different.
• Risk is present in all projects but becomes more pronounced in global projects where there are often new risks, particularly if the project is being built in a part of the world where security is an issue. In some countries, contract law is not well established and other local laws may not be well understood by other nationalities.
• Risks in communications and risks arising from misunderstandings and misinterpretation are much greater.
• Risks in communications and risks arising from misunderstandings and misinterpretation are much greater.
• There are differences of standards in many countries that can extend to attitudes towards health and safety. Design standards can vary and local factors such as climate, topography and infrastructure can dramatically affect a project. Local customs can also be bewildering, especially for staff living overseas where there might be different attitudes towards gifts, entertainment and hours of work.
• In many countries of the world, different ethical standards apply. This affects attitudes towards the law and, indeed, national laws can be very different in different territories. In some countries, bribery and corruption have become institutionalised and are the only means by which some local officials can earn a living.

Cultural Diversity in Project World - Can it be celebrated?

Cultural Diversity in Project World - Can it be celebrated?

Cultural influences are ofcourse nothing new. Any of us who have traveled to another country, the least to say to another state in our land of diversity, would have encountered some form of cultural differences in life.
In a mobile project world, it is quite a possibility that the project managers would end up working in a variety of cultures or work with people who reflect an array of multi-cultural perspectives. Projects around the world are found to showcase similar kinds of threats and opportunities that are non-technical and quite often identified as cultural.To name a few, some cultures invite very direct speech, while others abstain from it. Some cultures follow a very formal chain-of-command in terms of project communications, while other cultures promote a more horizontal flow of information.
A Project Manager working within a particular cultural environment will necessarily reflect that culture, both explicitly and implicitly. Now, is this a good reason to learn to value and celebrate the cultural diversity in one's project world?

Delhi Metro - Some Interesting Facts.

Delhi Metro - Some Interesting Facts.

I found out an interesting article on Delhi Metro in Live Mint "Off the record" column. The link is at http://www.livemint.com/articles/2009/08/30220005/Delhi-Metro-what-counts-what.html

I sensed a tinge of bias against Delhi Metro in general, and Sreedharan in particular, in the whole article.Nevertheless, it discusses some very interesting points, on lines of what we discussed about the urban metros in our class. I am jotting some points that i felt were interesting.

• Presence of a champion figure in E. Sreedharan.
• Some form of reduction in Vigilance and audit has helped the decision making to become a lot quicker.
• Huge tax exemptions and soft loans provided are a critical factor for the success.
• Land acquisition was done under emergency clause of Land Acquisition act ! (I do not know whether we can acquire land under emergency clause for metros anymore.)
• He also makes a point towards the end about replicability and development of second string of leadership.

It is interesting to note a lot need to be done to create a facilitating environment for such projects. Such things may not have been possible if the project was done PPP way. We will have to see how the other metros handle these issues, where Delhi Metro was benefited by some extra-ordinary privileges.

Bandra Worli sea link

Bandra-Worli Sea Link

Lessons to learn from

The Bandra-Worli Sea Link presents an interesting case-study of infrastructure planning and management issues, in line with our discussion on the Montreal Olympic Stadium. The sea-link was originally conceived of in 1960s, but received a green signal only in 1999, after studies were conducted by the Central Road Research Institute and the Mumbai Metropolitan Region Development Authority (MMRDA). The Maharashtra State Road Development Corporation (MSRDC) was appointed as the nodal agency for the project in 1999. The MSRDC awarded the project to the Hindustan Construction Company (HCC), but only to see a series of failure in meeting deadlines. The initial deadline was December 2004 which was later revised to December 2007 and then to December 2008. Actual work, however, did not commence until January 2005 when the Supreme Court gave the project go-ahead. The consequences of haphazard planning and scheduling, as was evident in the Montreal case, are reflected in this example as well.

The MSRDC changed consultants in 2003 and gave entry to Egypt-based Dar Consultants. The new party brought in tremendous design changes which escalated the costs by four times (Rs 4.4 billion to Rs 16.34 billion). HCC is said to have lost about Rs 4 billion due to these changes. Thus we see the role of designing and its crucial place in the overall implementation of an infrastructure project.

In April 2009, days before the completion of the project, three sets of sub-contractors threatened to pull out due to issues with the consultants. One of them, the Roman Tarmant Ltd., was about to obtain a contract for Polymer Modified Bitumen (PMB) surfacing to provide a water-proof road. However, the company backed out due to unreasonable conditions on warranty period. The wide spectrum of players involved in an infrastructure project and the corresponding human management that the size of such projects calls for is evident in this case.

A part of the rise in costs was due to the interests on borrowings and payment to the Municipal Corporation of Greater Mumbai for a casting yard, an instance that shows how economic factors can equally inflect a project just as any other. Also to be noted is the fact that around 4000 workers and 150 engineers from India as well as China, Egypt, Canada, Switzerland and Britain are said to have participated in the project, which would have demanded micro-level cultural integration, a pointed that was highlighted in the class.

A few local issues like environmental concerns and issues pertaining to the fishermen, also surfaced during construction, which, though parochial, could have impeded the completion of the project. The Bandra-Worli sea-link, however, managed to brush such concerns aside with active political support from the state. To epilogue, this project presents many of the nuances involved in infrastructure planning and shows the amount of meticulousness that the task calls for.

Sources:
Indian Infrastructure, July 2009
"Bandra-Worli Sea Link: A Traveller's Delight", The Economic Times, June 30, 2009
(http://economictimes.indiatimes.com/News/Economy/Infrastructure/Bandra-Worli-sea-link-A-travellers-delight-/articleshow/4718082.cms)
Official Website (http://www.bandraworlisealink.com/)

MIVAN formwork.

SYSTEM OF PRECAST CONSTRUCTION

An engineered system of building construction, namely “3-S” system was developed by B.G.SHIRKE CONSTRUCTION TECH LTD., for achieving, speed, strength, safety and economy in construction practices. The system involves structural elements such as pre-cast hollow column shells pre-cast concrete beams, light weighed reinforced cellular autoclaved concrete slabs for floor and roofs constituting the basic structural formwork. The “3-S” system involves activities for construction of building such as:

I. Cast in-situ sub-structure including foundations, stem columns, plinth beams, plinth masonry.

II. Erection of partial pre-cast components, jointing of these components using cast in-situ concrete with appropriate reinforcement.

III. Lying of reinforced cast in-situ screed over slab panels, construction of panels, construction of walling, flooring, plastering, water proofing etc.

Achieving the “3-S” system in the MIVAN formwork is quite easy. MIVAN formwork has got the unsurpassed speed of construction due to saving time for required time in masonry and plastering. The strength of raw aluminium is very less but when alloyed with other materials prove to be strong enough to use as a formwork . To ensure safety in the site, an integrated safety/ working platform is developed which ensures labor safety during erection and striking of the formwork. Economy is also one of the main factors of any system. The MIVAN formwork proves to cost efficient as it can be used efficiently for 250 times.

Present Technologies Available in INDIA

Some of the advanced technologies of formwork catering to the speed of construction are given below:

To name a few:-

1) The Prefabrication Technology

The Pre-cast concrete elements in roofs, floors and in walls have become more common as these eliminate shuttering; centering & plastering labor and saves material cost.

Prefabricated Technology (Raymond, 2001)

2) Tunnel Formwork Technology

It is a technology constructing large no of housing within short time using steel forms to construct walls & slabs in one continuous pour.

Tunnel formwork (Raymond, 2001)

3) Outinard Technology

Outinard’s superior engineering, the use of high quality steel and High Performance quality control result in a vastly superior Wall Form system.

Outinard Technology (Raymond, 2001)

4) Mascon Technology

The Mascon Construction System is a system for forming the cast in-place concrete structure of a building. It is also a system for scheduling and controlling the work of other construction trades such as; steel reinforcement, concrete placement, and mechanical and electrical trades.

Mascon Technology. (Raymond, 2001)

Computer Aided Planning for Tunnel Construction

Tunnels are subterranean conveyance systems. Historically tunnelling projects have suffered significant cost and time
overrun on account of variation in geological formation. Variation in strata may lead to various problems like tunnel
caving in, water seepage etc. An attempt has been made to extend the Q-system of rock mass classification for reliable
prediction of these tunnelling problems. For the purpose tunnelling problems have been identified and classified. A
computer tool has been developed to aid the process. Also simulation as an aid for time planning while tunnelling under
such varying geological conditions has been investigated. Reliable estimates of tunnelling problems and effect of
geological variations on the project schedule will help the project management in informed decision making as regards
issues like resource requirement. This paper describes the compilation and classification of tunnelling problems,
matching problems to the Q-system parameters and the simulation model developed.
Keywords: Tunnelling projects; Geological strata variation; Rock mass classification; Q-system; Project management
INTRODUCTION
Tunnels are used in the transportation sector for conveyance
of highway and railway traffic. They also serve as a means of
conveyance of water in irrigation and hydroelectric power
projects. During construction of tunnels variation of strata is
often encountered. This poses various problems in tunnelling.
Also, the decision regarding the support system required for
various strata is critical to ensure trouble free construction. As
the geological formation for each tunnel project is usually
very different and all scientific studies are carried on a project
specific basis, tunnelling in a new formation remains an art
than a science wherein the designers rely on intuition and
previous experience to effectively solve problems.
The Q-system is a system of rock mass classification1. This
system is essentially used in determining the support system
requirement for tunnelling under the prevalent geological
condition. The parameters of the Q-system are representative
of the geological conditions of the project. These parameters
have been used in predicting the problems likely to be faced in
tunnelling.
Manual calculation for Q-system is very tedious and time consuming.
This is significant considering the fact that the calculations
have to be done for every drill and blast cycle of the
tunnel construction, which may run into thousands for each
project. Thus a computer tool has been developed to aid in the
process which will save both time and effort.
H I Bidaiah is with International Metro Civil Contractors, 8 Jantar Mantar
Road, near Connanght Place, New Delhi 110 001; Dr K Varghese is with
Building Technology and Construction Management Division, Department
of Civil Engineering, Indian Institute of Technology, Madras, Chennai
600 036 while A N Mazumdar is with L&T-ECC Construction Division,
Mount Poonamallee Road, Manapakkam, PO Box 979, Chennai 600 089.
This paper was received on August 13, 2001. Written discussion on the paper
will be entertained till July 31, 2003.
Tunnels are typically constructed either using the drill and
blast method or by using tunnel boring machines. The
tunnelling operation is a repetitive process wherein the same
activities are repeated in each successive cycle. Also, it is
common practice to open up more than one face of a tunnel
for excavation, so that the project can be expedited. Thus, the
various activities fight for the same resource. This makes
resource allocation an important issue to be considered in
tunneling operations. This also influences the project
schedule.
As mentioned earlier one of the major uncertainties faced
during tunnelling is that of variation of strata. Initial
geological investigation gives a fair idea of the type of rock
that might be encountered. But uncertainty prevails and
makes time planning all the more difficult. Simulation can be
used as an effective tool to aid in planning as regards issues like
resource requirements while working under varying
geological conditions.
Q-SYSTEM
The Q-system1 of rock mass classification was developed in
Norway in 1974 by Barton, Lien, and Lunde all of the
Norwegian Geotechnical Institute. The Q-system is based on
a numerical assessment of the rock mass quality using six
different parameters
o Rock Quality Designation;
o Number of joint sets;
o Roughness of the most unfavourable joint or
discontinuity;
o Degree of alteration or filling along the weakest joint;
o Water inflow; and
o Stress condition.

Construction Planning

The development of a construction plan is very much analogous to the development of a good facility design. The planner must weigh the costs and reliability of different options while at the same time insuring technical feasibility. Construction planning is more difficult in some ways since the building process is dynamic as the site and the physical facility change over time as construction proceeds. On the other hand, construction operations tend to be fairly standard from one project to another, whereas structural or foundation details might differ considerably from one facility to another.

Forming a good construction plan is an exceptionally challenging problem. There are numerous possible plans available for any given project. While past experience is a good guide to construction planning, each project is likely to have special problems or opportunities that may require considerable ingenuity and creativity to overcome or exploit. Unfortunately, it is quite difficult to provide direct guidance concerning general procedures or strategies to form good plans in all circumstances. There are some recommendations or issues that can be addressed to describe the characteristics of good plans, but this does not necessarily tell a planner how to discover a good plan. However, as in the design process, strategies of decomposition in which planning is divided into subproblems and hierarchical planning in which general activities are repeatably subdivided into more specific tasks can be readily adopted in many cases.

From the standpoint of construction contractors or the construction divisions of large firms, the planning process for construction projects consists of three stages that take place between the moment in which a planner starts the plan for the construction of a facility to the moment in which the evaluation of the final output of the construction process is finished.

The estimate stage involves the development of a cost and duration estimate for the construction of a facility as part of the proposal of a contractor to an owner. It is the stage in which assumptions of resource commitment to the necessary activities to build the facility are made by a planner. A careful and thorough analysis of different conditions imposed by the construction project design and by site characteristics are taken into consideration to determine the best estimate. The success of a contractor depends upon this estimate, not only to obtain a job but also to construct the facility with the highest profit. The planner has to look for the time-cost combination that will allow the contractor to be successful in his commitment. The result of a high estimate would be to lose the job, and the result of a low estimate could be to win the job, but to lose money in the construction process. When changes are done, they should improve the estimate, taking into account not only present effects, but also future outcomes of succeeding activities. It is very seldom the case in which the output of the construction process exactly echoes the estimate offered to the owner.

In the monitoring and control stage of the construction process, the construction manager has to keep constant track of both activities' durations and ongoing costs. It is misleading to think that if the construction of the facility is on schedule or ahead of schedule, the cost will also be on the estimate or below the estimate, especially if several changes are made. Constant evaluation is necessary until the construction of the facility is complete. When work is finished in the construction process, and information about it is provided to the planner, the third stage of the planning process can begin.

The evaluation stage is the one in which results of the construction process are matched against the estimate. A planner deals with this uncertainty during the estimate stage. Only when the outcome of the construction process is known is he/she able to evaluate the validity of the estimate. It is in this last stage of the planning process that he or she determines if the assumptions were correct. If they were not or if new constraints emerge, he/she should introduce corresponding adjustments in future planning.

Earth Building

Mudbrick, also referred to by the Spanish name of 'Adobe' which means mud or puddled earth, generally refers to the technique of building with sun-dried mud blocks in either load bearing or non load bearing construction. Mudbricks are becoming increasingly commercially available in a range of stabilised and non stabilised bricks.

Mudbrick has several advantages over conventional fired clay or concrete masonry. The advantages include:

• Low in embodied energy
• Utilisation of natural resources and minimal use of manufactured products
• Good sound absorption characteristics
• High thermal mass
• A claimed ability to "breath"
• Suited to a wide range of soils
• Easily manufactured and worked
• Flexibility in design/colour/surface finishes
• Insulation properties similar to those of concrete or brickwork

Mudbricks are typically 250 mm wide x 125 mm high x 375 mm long and normally made from earth with a clay content of 50 to 80% with the remainder comprising a grading of sand, silt or gravel. Kaolin clays are the preferred clay types due to their non expansion characteristics. Stabilising the mudbrick with straw or other fibres is sometimes employed where the soil mix displays excessive shrinkage behaviour. Cement and bitumen stabilising is also used with the latter particularly effective in waterproofing.

From an engineering viewpoint, mudbricks typically have compressive strengths of around 1 to 2 MPa and need to posses a demonstrated resistance to erosion and cracking before being accepted for construction. Mortar for mudbrick laying is either a traditional sand/cement mortar or a fine aggregate soil mortar preferably made from the same parent material as the mudbrick units.

Finishing of mudbrick walls can be undertaken with a variety of techniques ranging from as constructed to a simple "bagged" finish to a full set earth render. Linseed oil is commonly used to seal the exterior of as constructed mudbrick.

Value Engineering

Value engineering may be broadly defined as an organized approach in identifying unnecessary costs in design and construction and in soliciting or proposing alternative design or construction technology to reduce costs without sacrificing quality or performance requirements. It usually involves the steps of gathering pertinent information, searching for creative ideas, evaluating the promising alternatives, and proposing a more cost effective alternative. This approach is usually applied at the beginning of the construction phase of the project life cycle.

The use of value engineering in the public sector of construction has been fostered by legislation and government regulation, but the approach has not been widely adopted in the private sector of construction. One explanation may lie in the difference in practice of engineering design services in the public and private sectors. In the public sector, the fee for design services is tightly monitored against the "market price," or may even be based on the lowest bid for service. Such a practice in setting professional fees encourages the design professionals to adopt known and tried designs and construction technologies without giving much thought to alternatives that are innovative but risky. Contractors are willing to examine such alternatives when offered incentives for sharing the savings by owners. In the private sector, the owner has the freedom to offer such incentives to design professionals as well as the contractors without being concerned about the appearance of favoritism in engaging professional services.

Another source of cost savings from value engineering is the ability of contractors to take advantage of proprietary or unusual techniques and knowledge specific to the contractor's firm. For example, a contractor may have much more experience with a particular method of tunneling that is not specified in the original design and, because of this experience, the alternative method may be less expensive. In advance of a bidding competition, a design professional does not know which contractor will undertake the construction of a facility. Once a particular contractor is chosen, then modifications to the construction technology or design may take advantage of peculiar advantages of the contractor's organization.

As a final source of savings in value engineering, the contractor may offer genuine new design or construction insights which have escaped the attention of the design professional even if the latter is not restrained by the fee structure to explore more alternatives. If the expertise of the contractor can be utilized, of course, the best time to employ it is during the planning and design phase of the project life cycle. That is why professional construction management or integrated design/construction are often preferred by private owners.