2376

	ment of water and debris. To totally			arch ribs, bracing, and floor - was veri-
	close the ends of the tubular shapes,			fied by wind tunnel tests.
	horseshoe-shaped plates were welded			Erection
	to the ends of the tubes.
	At the portals, the K-bracing was ter-
	minated with a three-dimensional X-			Erection of the bridge was accom-
	shaped connection. The multi-jointed,			plished using temporary towers resting
	three-dimensional intersection of the			on the arch footings and a system of
	bracing was achieved by welding			bridge strand backstays and forestays.
	plates into an octagon and welding the			Hydraulic jacks in the stays allowed
	ends of the tubes to the sides of the oc-			alignment adjustments to be made dur-
	tagon. More than 760 m of fillet welds			ing erection.
	were used to make up the bracing.			The erection progressed by lifting and
	Another part of the bracing system is a			bolting successive 15.2 m long welded
	2.1 m square welded box strut between			steel rib sections into place with a
	arch ribs directly below the roadway at			barge-mounted crane floating on the
	each end of the bridge. Access to the			lake. As adjacent rib sections were
	interior of the ribs is through lockable			placed, the welded tubular K-bracing
	doors in these boxes. Electrical distrib-			was installed to maintain alignment
	ution centers are also inside the struts.			and rigidity of the ribs. Shop fabrica-
	The floor system for the 11.5 m wide			tion accuracy was maintained so well
	roadway	consists	of longitudinal	that there were no mismatches during
	stringers, supported on welded I-girder			erection.
	floor beams. Floor beams are spaced at			Owner:
	15.2 m centers and are hung from the
	arch ribs with eight wire ropes, four at			Arizona Dept of Transportation
	each end of a floor beam. Welded steel			Engineers:
	girders 2.0 m deep are used as exterior			HNTB Corp., Kansas City, MO
	stringers and also function as stiffening			Main contractor:
	girders	for aerodynamic ''stability.		Edward Kraemer & Sons, Inc., Plain,
	About 2.1 m of fillet welds were re-			WI
	quired to fabricate the floor system.			Service date: 1990
	The overall stiffness of the system -
	BRIDGE SCOUR FAILURES			Introduction
	D.V. Mallick M.M.Tawil
	Technical Advisors			Failure of a bridge is viewed seriously
	National	Consulting	Bureau, Tripoli,	by the public since it involves not only
	Libya			traffic disruption and the loss of tax
				payer's money but can also result in

203

loss of human lives. It reflects on the		covered by load or safety factors are
reliability of the design procedures as		revealed in weaknesses after construc-
well as on the quality of construction.		tion. Geotechnical investigations are
Use of poor construction materials and		very important for the design of bridge
inadequate design	assumptions are	foundations.
generally this suspects. Designers and		This paper describes a case history of
contractors have to be extra cautious		failure of three reinforced concrete
while designing	and constructing	(RC) highway bridges built across
bridges to resist the effects of natural		Wadi El Nagah watercourse in the
hazards like floods, earthquakes and		northeastern part of Libya. Two out of
landslides in addition to normal traffic		three bridges collapsed and one suf-
loads. Studies have been made in re-		fered damage that could be repaired.
cent years to understand the pattern of		All these bridges have been victim of
occurrence, of these natural phenome-		heavy floods in the wadi, which caused
na statistically, attempting to compute		severe damage due to scour, erosion
probability of their future occurrence.		and undermining of the soil below the
The cumulative effect of various as-		foundations of intermediate piers and
sumptions and approximations intro-		the abutments. In all cases, parts of the
duced at the analysis and design stage		approach road embankments were also
of a bridge which are not sufficiently		washed away.

Fig. 38

204

Description of the Bridges

The location of three bridges built across Wadi El Nagah are shown in Fig. 38. The catchment area of the wadi across which these bridges were built consists of hilly terrain. Mean annual rainfall precipitation in this region is around 400-600 mm. Almost all the precipitation occurs during the winter months, from October to January of each year.

Bridge A, built about three decades ago, consisted of three simply supported spans of pre-stressed reinforced concrete beams supported on two central piers and two end RC abutments. The foundation of all these supporting elements consisted of shallow block foundations. Bridge B was a bowstring girder RC bridge supported on two massive intermediate plain concrete pillars and anchored at both ends to earth fill embankments. Bridge C, part of the new coastal highway, consisted of an RC portal frame with propped overhangs. Vertical supporting members of the portal are shear wall type piers 10 m high and 0.7 m X 6.0 m in cross section. The foundations of these piers consisted of RC blocks 10 mX 5 mX 1.5 m resting on plain concrete mats of 300 mm depth and located 4 m below the planned wadi bed level. The RC abutments of this bridge were embedded in the approach road embankments at both ends. Gabion protection was provided as per the design.

Damage Assessment

Bridge A was badly damaged by the flood water. One abutment collapsed

and the beams at that end of the span were twisted. Foundation blocks of the intermediate piers were exposed. Part of foundation soil of the far end abutment eroded away, leaving the foundation block partially suspended. Expansion joints between the concrete deck sections over the intermediate supports widened considerably due to distortion and the lateral displacement of the bridge decks.

The old multispan RC bowstring girder Bridge B totally collapsed. Its two intermediate plain concrete supporting piers overturned sideways along with the foundation blocks and moved downstream to Bridge C.

The new Bridge C did not suffer any appreciable structural damage although scouring of the wadi bed, accompanied by undermining of the soil below the foundation blocks of the vertical piers and the east RC abutment did occur, leaving them partially suspended (Fig. 3). The approach connection to the bridge deck from the east was destroyed due to the collapse of the approach concrete slab caused by erosion of the earth fill at the back of the abutment. This bridge has been repaired and opened to traffic.

Causes of Damage

Scour of the wadi bed, undermining the soil below the intermediate piers and the abutments' foundation blocks, and the erosion of the approach road embankments during a heavy flood, were the causes of the damage and collapse of these bridges. This is not the first time such damage has occurred.

205

"Bridges are vulnerable to natural hazards ranging from hurricanes to earthquakes. But scour is the problem that has caused more bridges to Mil than all of rest combined. One study... concluded that among 86 bridge failures [in the USA] from 1961 to 1976, 48 were due to floods. Out of 48, 46 were due to bridge scour" [1]. Another recent survey revealed 494 of the 823 bridge failures in the USA from 1951 to 1988 were primarily the result of scour of foundation material [2].

In addition, some other circumstances aggravated the damage and led to collapse of one of these bridges. The damages occurred partly due to shortcomings of the design and partly due to ignorance of the effects of a temporary road embankment across the wadi about 500 m upstream from Bridge A [3]. This temporary road embankment acted like an earthfill dam across the wadi, creating an artificial lake upstream. Due to heavy floods, this dam' gave way, releasing a flood with a fast moving flow of water about 12 m high, as observed from the water marks on the soffit of the deck of Bridge C, resulting in erosion and undermining scour of the wadi bed and the side embankments. The damage to Bridge A was severe due to its undesirable location at a bend in the wadi, as shown in

Fig. 38.

Rehabilitation

Two of the three bridges on Wadi Al Nagah were abandoned and the third, Bridge C, has been rehabilitated. The main problems in rehabilitating Bridge

C were to support the foundation blocks of one intermediate pier and one abutment, and to provide a new reinforced concrete approach road slab.

The repair work had to be planned very carefully in order not to disturb the structural safety of the other parts. of the bridge. The sequence of the repair work consisted of removing loose and eroded soil from below one side of the foundation block at a time, thorough compaction of the base and measuring any deflection of the suspended part of the foundation block. This part was then block concreted.

Similarly, the other side of the pier was prepared and block concreted.

To ensure proper contact between old and the new concrete blocks, epoxy mortar was injected between them. Then the central part below the foundation block was cleared of all soil deposits. Precast concrete beams were inserted on the prepared base. Finally, the end sections were grouted, thus providing another foundation slab to the existing foundation block. A similar procedure was adopted for the repair of the abutment foundation. The depth of the new foundation system was based on scour depth calculations. After carrying out all necessary repairs for rehabilitation, the wadi bed and approach road embankment slopes were suitably protected. This bridge has now been operational for two years. The owner was advised to dismantle Bridge A, so as to provide a clear path for the wadi stream approaching Bridge C. To date, this damaged bridge has not been removed.

206

Lessons					- Location of a bridge near a bend in a
					stream should be avoided.
- Bridge planning and design is not					-	There is a need for research to es-
only a job of structural engineer, but is					tablish		the	relationship		between
the joint responsibility of a team of					flow depth, flow velocity and total
structural, hydrology and geotechnical					scour depth for actual conditions in the
engineers. Structurally well				designed	field.
bridges have failed as a result of hy-					References
draulic conditions, primarily due to
scour of foundation material.					[1] MURILLO, J. A. The Scourge of
-	The uncertainty of collecting proper
hydrological data, the probability of					Scour. ASCE Civil Engineering, July
occurrence of future severe storms and					1987, pp. 66-69.
their effect on the bridge system re-					[2] HUBER, F. Update: Bridge Scour.
quire		advance	preparation for all		ASCE		Civil	Engineering,		September
eventualities.					1991, pp 62-63.
-	Initial evaluation of scour vulnera-				[3]	MALLICK,D.V.;			ELWAFATHI,
bility of streambed material is es-					A.M.
sential. Due to the stochastic nature of					Damage Study of Three Reinforced
the		hydraulic parameters		involved	Concrete Bridges over Wadi El Nagah,
in bridge design, appropriate scour					Libya. Conference on Our World in
countermeasure programmes, like in-					Concrete & Structures, Vol. VI
stalling riprap, guide banks to protect					(1987),		Singapore, 25-26 August
abutments and			embankments and		1987, pp 50-66.
sheet piling along the face of piers
and/or abutments, must be clearly
planned in advance.
A NEW FOOTBRIDGE, AUSTRIA
					Graz. Austria, have an elevation dif-
Harald Egger,					ference of about 2.2 m. The designers
Prof. Dr Hermann Beck, Research As-					felt that a simple straight beam in-
sist.					clined across the river at this point
Univ. of Technology Graz, Graz, Aus-					would		be aesthetically		unsatisfactory.
tria					They therefore opted for spanning the
Design					river with a beam that was slightly ele-
					vated at its centre and horizontally
					supported by columns, with its upper
At the site selected for a new foot-					surface serving as a footpath.
bridge, the banks of the Mur River in

207

Fig. 39

footpath divides "before leading down to the left and right. The aim of designing a fine-membered bearing structure led to the development of a compound beam construction comprising a stiffening member, with a tensioning member and a compression member on the underside of the bridge (Fig. 39).

The height and width of the stiffening member decrease toward the centre of the bridge from the supports at either end, i.e., toward the compression member. The shape of the composite prismatoid thus also determined the spread of the tensioning member underneath toward its supports.

In accordance with the geometry and design principle of the entire construction, the bridge deck has been designed as a folded plate structure forming an integral part of the bearing system. On one bank the deck rests upon the body of the, stiffening member; on the other bank it extends from the stiffening member's sides.

The bearing structure of the bridge rests on two pairs of columns on the banks of the river, cantilevering on either side. On the right bank it extends to the old non-bearing embankment wall, while on the left-hand bank the body of the stiffening member ends in a cantilever design, with the walking deck extended from it to permit direct access to the footpath without ramps or stairs.

Construction

The stiffening member of the bridge covers an effective span of 55.8 m. Its cross section has a height of 2.0 m over the columns and 0.7 m at the Centre. The bridge deck, a hollow steel plate, is folded on its lower side and forms part of the stiffening member. The deck is connected asymmetrically to the trilateral body of the stiffening member in relation to the centre of the bridge. On the left side of the bridge its

208

top follows the top edge of the stiffening member; on the right side, starting from the centre of the bridge, it intersects with the lateral surfaces of the prismatoid, parallel to its bottom edges. The compound stiffening member is also asymmetrical. Its characteristic cross section is shown in Fig. 40.

Fig. 40

The walls of the trilateral prismatoid are 15 mm thick over its entire length, but its longitudinal braces - an additional flange plate welded where the bridge deck begins to descend - were adapted to the asymmetry of the stiffening member, as was the quality of the plate used. The trilateral prismatoid is reinforced by transverse bulkheads placed 2.2 m from each other, corresponding to the folds of the cover plate of die bridge deck. The entire structure is sealed airtight. All parts, whether assembled in the shop and at the site, were joined by welding.

In order to make sufficient allowance for floodwaters, the tensioning member underneath the bridge has a very flat design, with the elements spreading out from the centre to the supports, where they are eccentrically connected

to the stiffening member. This spreading is a consequence of the geometrical configuration of the bearing structure and design considerations. Stability of the stiffening member is also improved by this expansion and by the eccentric connections, the latter also reducing deflection of the stiffening member.

To achieve the required stiffness for the entire compound bearing structure, 145 mm thick bands of grade Fe 510 steel were used for the tensioning member. These relatively heavy bands were attached to the stiffening member at the quarter points of the central bridge span and supported against wind loads. The connection of the tensioning bands to the compression member shown in Fig. 41, which illustrates both the solution originally required by the invitation to tender and the final method employed by the contractor. Behind the supports, the bands were anchored to angle cleats that were laterally welded to the sleeve plates of the stiffening member. The steel bands were stretched in place, but not prestressed.

The stiffening member rests on four slender free-standing columns. It is fixed to one column, and longitudinally movable but transversally fixed to the other three so that all four columns may contribute to the transmission of wind loads. In addition, the entire bearing structure resting on the columns is protected against transverse wind attack from below.

For reasons of time and cost, the bearing structure of the bridge, which put heavy demands on manufacturing skills, was produced at the plant. It was

209

manufactured in large sections which were then transported by road to the site, in part with the bridge deck already attached to the bearing structure.

Fig. 41

on the river's banks, and hoisted into position by an automobile crane. Erection was accomplished in three nightshifts. The sections were placed on a temporary support and the entire bearing structure was then joined together by welding. After a final insertion of the tensioning member on the underside of the bridge, the auxiliary support was removed.

Architects:

G.Domenig and H. Eisenköck, Graz, assisted by G. Wallner

Civil Engineers:

H.Egger, Graz, assisted by H. Beck

Contractors:

Alpine Bau (concrete), Salzburg Vöest-Alpine (steel), Linz

Service date: 1993

These sections were assembled into larger units, whenever possible directly

IS ISO 9001 EFFECTIVE FOR ENGINEERING CONSULTANCIES?

Jørgen Laustsen, Civil Eng. Copenha-	on a large scale - but mostly for the
gen, Denmark	sake of marketing.
	Attitudes towards ISO 9001 among
The quality assurance processes de-	English, German and Danish consult-
scribed in ISO 9001 have not been	ing engineers were the subject of a re-
greeted with unanimous enthusiasm by	cent research study [1]. The study is
consulting engineers. Consultants in	based on interviews with twenty-nine
England, Germany and Denmark have	consulting engineering companies and
in fact responded quite differently to	institutions. Thirty-five additional
the ISO 9001 quality assurance stan-	companies responded to questionnaires
dard. Danish engineers have generally	on the subject.
declined to adopt the standard, the	Criticism in Denmark
Germans are decidedly more keen on
their own DIN standards, whereas the
English have sought ISO certification	In Denmark the Association of Con-
	sulting Engineers (FRI) has rejected

210

the ISO standard, arguing that it does	with it. Additional companies had be-
not cover all the critical elements of a	gun to implement the standard. This
knowledge-based service. As a conse-	tendency is substantiated by a survey
quence of this position, dialogue be-	of the European Construction Institute
tween ISO and FRI has ceased.	(ECI), 52 % of whose members -
Only one consultancy had been certi-	contractors, consultants and clients -
fied in accordance with ISO 9001. The	replied that they were certified, while
majority of companies have instead es-	11 % were in the process of imple-
tablished a quality assurance system	menting the standard, and 16% ex-
based on the paragraphs in the standard	pressed the wish to do so.
that seemed relevant, supplementing
them as required. Several companies
have likewise produced cross refer-
ences to the ISO standard, as some cli-
ents have demanded a quality assur-
ance system in accordance with the
ISO standard. The standard is, there-
fore, used - but always as a reference.
Doubt in Germany
In Germany, the ISO standard has only
recently been introduced and until now
only a few contractors have im-
plemented it. As yet, no engineering	Fig. 42
consultancy has done so. Several con-
sultants stated that they could not un-	In conversations with English consul-
derstand the necessity of the ISO stan-	tants it was not unusual to hear that
dard. The general opinion of those	they had/in fact, no expectations for
questioned was that the way the Ger-	substantial positive effects from imple-
man construction industry and the DIN	menting the standard. It is seen as a
standards are related makes the ISO	necessary evil, one which enables con-
standard superfluous.	sulting engineers to qualify for projects
Activity in England	where the client demands the ISO
	certificate. The standard and the quali-
	ty assurance system it promotes are
The attitude towards the ISO standard	thus seen as a dubious formality, use-
(BS 7550) in England differs dramati-	ful only as a marketing tool.
cally from the other two countries	The real value of ISO certification
studied. Nearly 40 % of the companies	seems limited. Both clients and consul-
in the survey had implemented ISO	tants who were surveyed agreed that
9001 and were certified in accordance	ISO 9001 certification does not actual-

211

ly ensure better quality, but only that					sultancies. The standard was drawn up
certain	documented guidelines			had	for manufacturing companies with tan-
been followed.					gible end-products. As the standard
In England, a small industry has grown					only covers the critical processes for
up around the standard. Around 6000					that type of production, it is not certain
persons now work on implementing,					that it is suitable for knowledge-based
certifying and maintaining quality as-					services like an engineering con-
surance systems.					sultancy. The critical processes are not
No Extra Fee					necessarily the same, so the question
					is: How relevant is the standard for
					consultancy. This can be illustrated in
Is a client willing to pay extra for this					Fig. 42.
extra initiative? A survey carried out					The differences between product-based
by Prof. Peter Barrett, Salford Univer-					and knowledge-based endeavors are
sity, England, shows that only 3% of					considerable. The main reason for this
clients take quality assurance into ac-					is the cognitive and iterative aspects of
count when they select consultants. 95					consultancy. The process is difficult to
% of the cornpanies and clients sur-					forecast	and	schematicise, which
veyed did not expect a higher price for					makes it problematic to assure quality.
the services of a certified company.					The process of the work of an engi-
Many employees still repudiate the					neering consultancy is illustrated in
quality assurance system, and many					Fig. 43.
companies are still not working consci-
entiously with the system. There is, for
example, no		widespread information
about the costs of ISO-certified quali-
fy. In all three countries, only the ex-
penses of internal and external audits
are registered. Only in Denmark are
expenses such as compensation and
reparations		registered. In	all	three			Fig. 43
countries, however, there is no existing
standard	as an alternative		to the ISO		Revision of ISO 9000
9000 standard.
Is ISO	9001 Applicable		for	Engi-	The complications stemming from the
neering Consultancies?					iterative	work	process has been con-
					sidered by the ISO/TC 176 Task Force
Given the scepticism of so many of the					when it started to revise the ISO 9000
respondents in the study, it is reason-					standard. The standard has been split
able to question if the ISO standard is					up into four main areas:
indeed applicable for engineering con-					- Hardware

212