25 Iunie 09 Sakata Footbridge

8/13/2019 25 Iunie 09 Sakata Footbridge

1/8

DESIGN AND CONSTRUCTION OF SAKATA-MIRAI FOOTBRIDGEUSING REACTIVE POWDER CONCRETE

Yoshihiro Tanaka Hiroyuki Musya Akio Ootake Yoshihide Shimoyama Osamu Kaneko

Taisei Corporation Taiheiyo Cement Corp. Maeta Concrete Ind.

JAPAN JAPAN JAPANKeywords:fiber reinforced ultra strength concrete, heat treatment, wet joint, outer cable

1. INTRODUCTION

Fiber reinforced reactive powder concrete under the brand name Ductalhas not only out of range

unique mechanical properties but also strong durability. Because of the ultra high compressive,

bending and tensile strength, the concrete bridge made of this material can enormously reduce the

dead weight and this results in that the dimension of the foundation becomes very small. Therefore

the total construction cost of the bridge can be probably reduced depending on the bridge span or the

soil condition though, compared with the pre-stressed concrete bridge using the ordinary concrete.

Additionally, the life cycle cost of the bridge made of this material can also be reduced because of the

strong durability.

The actual applications of reactive powder concrete have been done by around 20 projects in the

world and two of them were the bridge construction [1], [2]. In this paper, the design and construction

process of Sakata-Mirai Footbridge, which is the first application in Japan, are discussed to establish

the future guideline for design and construction. The span of Sakata-Mirai Footbridge is 50m and the

width is 2.4m. Taking account of the efficient application of mechanical advantages of Ductal,

Sakata-Mirai Footbridge was designed as a boxed type cross section with perforated webs, therefore

the self-weight super-structure resulted in about 1/4 of the ordinary pre-stressed concrete bridge. In

order to verify the new conceptual design method, the fundamental beam test with/without wet joint

beam loading experiments as well as the prototype model loading experiments have been conducted.

Furthermore, the mixing process of an ordinal mixing batch plant and the casting control methodology

has been confirmed using the prototype segments.

2. MATERIAL PROPERTIES OF DUCTAL

2.1 Fresh properties

The basic formulation of Ductal for Sakata-Mirai Footbridge is given in Table 1. Basic principles is

based on RPC200 (Reactive Powder Concrete 200MPa) [3].The major principles are as follows; 1)Minimum of defects such as micro-cracks and pore spaces by extremely low water/cement ratio, 2)

Enhancement of compacted density by optimization of the granular mixture, 3) Enhancement of the

microstructure by heat treatment, and 4) Enhancement of ductility by incorporating steel fiber. The

self-leveling performance is achieved that a flow value (JIS-R-5202.11) is around 240 mm for the

material temperature of 20~25oC even for including the steel fiber (0.2 mm diameter x 15 mm) by 157

kg/m3(2% in vol.) in the matrix. Therefore it is possible to cast it into the very thin shell mold or into the

complicated shaped mold. The segregation or sinking of steel fiber from the matrix does not occur

because of viscousity of the paste. However it is noted that the orientation of the steel fiber should bedisturbed in all directions when casting. Any types of mixer including a double shaft pug mill or a pan

type can be used to mix Ductal. The mixing time depending on the ambient temperature is usually 12 to

14 minutes and the time available for placement is 2~3 hours. The initial and final setting time is also

depending on the ambient temperature and 30~32 hours.

2.2 Mechanical properties

The mean compressive strength value of Ductal is 238MPa with 90

o

C heat treatment for 48 hours.Figure 1 shows a typical load bending stress-deflection graph of a beam under three-point loading. The

specimen beam is 4x4x16cm in size and it is cured for 48 hours in 90oC. The flexure property exhibits

Table 1 Composition of Ductal

Session 1

417

Big projects and innovative structures


2/8

linear behavior up to its first crack stress

(25~30MPa), a post-first-crack strain

hardening phase up to its ultimate flexural

stress (40~45MPa), and a post-ultimate-load

strain softening phase. The first initial crack

stress mainly depends on the flexural

toughness of cement matrix and the ultimatebending stress depends on the bridging effect

of steel fiber, which is due to the fiber-matrix

bond as well as the tensile strength of fiber.

The steel fiber is 0.2mm in diameter, 15mm in

length and 2800MPa in tensile strength. The

incorporation of small-size steel fibers results

in ultra-high energy absorption capabilities.

The bending fracture energy is 36,000Nm/m2,

on the other hand one for ordinary concrete

with 30~50MPa in compression strength is at

least a range of 50~200Nm/m2. The direct

tensile test is very difficult and its test results are scattering so much that the tensile strength isestimated dividing the flexural strength by 4.2 [4].

Hence, the high-tensile strength combined with ductility makes conventional reinforcement

unnecessary for the construction of structural elements. The 15mm fibers inside of the cement matrix

act as if the steel rebars perform to resist for tensile stress in relation to the small size of the largest

grains. It makes it possible to employ very thin shell or complicated shaped members to design and

assemble sophisticated bridges.

The bond property is also excellent. The bond strength for steel rebar D16 and D32 is 65MPa and

71MPa, respectively. If this material were applied for the joint members, joint rap length could be

extremely reduced because of high-bond.

2.3 Durability

Because of the densest packing mixing design of the grain particles and the minimum mixing water

to hydrate with cementitious material, it includes extremely low porosity and it results in ultra highperformance durability. For severe exposure environmental test such as 300 cycles freezing and

thawing test, It provides no damage compared with conventional concrete or even with high

performance concrete. Penetration of liquid or gas is nearly non-existent in comparison to ordinary

concrete. It is impossible to obtain the water permeability coefficient by usual input permeability test

method. The input permeability method injecting 200~300MPa pressurized water into the specimen

provided the permeability coefficient will be smaller than 10-13

~10-12

cm/sec. The future technical

development of the permeability test method is requested for this material. The chlorine irons diffusion

coefficient 0.0019cm/sec was obtained by the 6 months penetration test soaking the specimens into the

artificial salt water. We are now carrying out the durability test exposing the samples on the coastal

zone. Abrasion test was also conducted by ASYM-C-779. The abrasion resistance is 2.3 times of

ordinary concrete and 1.8 times of granite.

3. FUNDAMENTAL DESIGN CONCEPT

3.1 Deign condition

Sakata-Mirai Footbridge is planed to replace the old pre-stressed concrete pedestrian bridge that

was built about 40 years ago crossing over the first class Niita River located in Sakata city, Yamagata

prefecture. Therefore, the following restrictions are requested to design and construct the new bridge.

1) The level and slope to the connecting road can not be changed.

2) The bridge bottom line should have 0.6m clearance from the high water level.

3) The longitudinal slope of the bridge should be less than 5%.

The limit state design method was basically employed for this project, and material constitutive laws

and checking method for each limit state condition were followed by Design rules for DUCTAL pre-

stressed beams published by Bouygues [4] in France. A part of the load factors for the ultimate limit

states was according to Japanese standard code of bridge and road.

3.2 Design flow chart

Fig. 1 Flexural behavior of Ductal

Proceedings of the 1st fib Congress

418


3/8

The design flow chart for

Sakata-Mirai Footbridge is

illustrated in Fig. 2. The

service limit states (SLS)

and the ultimate limit states

(ULS) are considered. The

tensile members due toSLS are not allowed to

generate any cracks, on

the other hand the tensile

members due to ULS are

allowed to generate cracks

but they have to sustain the

ultimate limit state load by

bridging steel fibers.

The finite displacement

and non-linear FEM

analyses consi dering the

material

constitutive laws were conducted for the detailed check of ultimate limit states. In order toeffectively proceed the design calculation, a preliminary design and a detailed design are separated for

each step. Especially for the perforated webs and the anchorage for the pre-stressing tendons, non-

linear FEM analysis is most effective way to solve the problem.

3.3 Structural concept

From a point of view of the first class river management and the prevention of boats crush accidents,

old piers for bridge had better be removed and one long span bridge is chosen to design. Because of

the three restrictions described above, the bridge height at both ends should be less than 55cm.

Therefore the lower deck typed bridge was taken into consideration. However, as the cross section is

open, then the web is weak for buckling and the torsional rigidity will be lack for pre-stressing or windloads. Finally, the upper deck typed bridge with variable height webs and closed box type cross section

has been decided to design. The general view of whole bridge is illustrated in Fig. 3 and the schematic

Fig. 2 Design flow chart for Sakata-Mirai Footbridge

Fig. 3 General view of Sakata-Mirai Footbridge

Photo 1 Schematic view of Sakata-Mirai Footbeidge Fig. 4 Middle cross section

Session 1

419



4/8

middle cross section is drawn in Fig. 4. The schematic completion view of final Sakata-Mirai Footbridge

is shown in Photo 1.

In order to take full advantage of the characteristics of Ductal and especially to use it without any

passive reinforcement, the structural concept and unique points of Meta Footbridge are as follows.

1) All pre-stressing cables are set outside of the cross section with deviators.

2) The deviators also play an important role in the diaphragm.

3) The perforated webs are employed for the sake of design view and reduction of dead weight.4) Eight pre-cast blocks are transversely and longitudinally by wet joint and post-tension cables.

5) No passive reinforcement by rebars even for the pre-stressing anchorage.

6) The cross-sections with variable web height are employed to effectively resist for the load.

The pre-cast blocks are composed of two types of segment blocks; i.e. one is closed form cross-

section described 1L, 2L, 1R and 2R in Fig. 3, and another one is open form cross-section that is

divided the former type into half described 3L and 3R. Each pre-cast block will not be produced by

match casting method but by individual casting method, then the dimensional errors of the completion

pre-cast blocks can be adjusted by wet joint.

Finally, the total dead weight results in 560kN and the total concrete volume becomes 22m3due to

the technical design efforts and material advantages. If ordinary pre-stressed concrete were applied for

this bridge, then the total dead weight would become 2780kN.

3.4 Stress verification due to SLS and ULS

In the preliminary design stage to determine the principal dimensions of each member, it had better

neglect the circular holes in the webs to calculate the stress in the webs and the flanges. However it is

noted that the shear stress check in the perforated web should be roughly calculated for the averaged

web height considering lack of the circular holes.

Applying the design load (Dead load + Live load) (=D+L) on the bridge for SLS, the results of the

bending and shear stress are illustrated in Fig. 5. The magnitude of the live load is 3.5kN/m2. The

bending stresses for both upper and lower flanges are satisfied the limit stresses f t=-8MPa and

0.6fc=108MPa. The shear stresses for SLS are checked by the following equations;

where = shear stress, fc= compressive strength characteristic value (=180MPs), ft= tensile strengthcharacteristic value (=-8MPs), x = mean compressive stress due to longitudinal pre-stressing, t =mean compressive stress due to transversal pre-stressing. These two formulas are similar to that used

in the French code (BPEL 91, Art 7.2) except the factor 0.4 which became equal to 0.25. This factor is

higher to that one used for ordinary concrete, but not so much; the ratio equals (0.4/0.25)0.5

= 1.26.

For ULS the verification check is conducted by more severe load conditions either (1.3D + 2.5L) or

(1.7D + 1.7L). Figure 6 demonstrates the verification check of bending moment and shear stress for

ULS. The maximum resistant moment of each bridge section are calculated by using the compressive

and tensile strength constitutive laws [4], which is illustrated in Fig. 7 and Fig. 8. The shear stresses

for ULS are checked by the following equations;

where u = maximum shear stress in the section at ULS, f fu = tensile strength characteristic valuecontributed by steel fibers (=-5MPa), b= safety factor (=1.3), Ftu= transversal pre-stressing, bn= width

of the web, St = spacing of transversal pre-stressing, u= angle between the cracking plane and theaxis of the web and its value should be greater than 30

o, xuand tu= compressive stress at ULS due to

2 x t 0.25 ft [ ft +2

3( x+ t)] (1)

u 11.25 0.85b 1.14 fc 2 / 3

sin 2 u (4)

tan 2 u = 2u/ (xu tu) u 30o

(5)

2x t 2 ft

fc

[ 0.6 fc ( x+ t)] [ fc

+2

3( x+ t)] (2)

ffub

u0.16

1.25 fc

tan u Ftu

b nSt

(3)


420


5/8

the longitudinal and transversal pre-stressing.

3.5 FEM analyses considering perforated web

For the detailed design step, 3 dimensional FEM analyses for 1/2 modeling whole structure taking

into account of the circular holes on the web have been conducted. Elastic FEM analysis is employed

for SLS and non-linear finite displacement 3 dimensional FEM analysis for ULS. The results of those

analyses make it clear that the circular hole effects on the stress field in the web. The results are also

used for the check of wet joint stress, the deflection in the middle span of the bridge due to the live load

and the effects of the deviators on the final maximum load resistant capacity. FEM analysis code is

DIANA and the material constitutive laws are illustrated in Fig. 7 and Fig. 8.

The longitudinal stress distributions near the middle of the bridge span with/without the circular holes

are illustrated in Fig. 9 for SLS. It is our design rule that

the wet joint connecting longitudinal direction; that issegment block 1L and 1R, can not sustain any tensile

stresses at all. The longitudinal stress distribution

without the circular holes is just linearly changing

along the web height, on the other hand one with

circular holes is observed as follows; i.e. 1) on the

middle center of the holes, the longitudinal stress

distribution increases near the hole edges, 2) however

on the middle line between one hole and another, the

longitudinal stress distribution reversely decreases

near the middle height of web. It is verified that all

stresses along the wet joint are compressive even for

the case of the circular holes. The maximum deflectionin the middle of span is 85mm that satisfies

deflection/span ratio 1/600.

Fig. 5 Verification for SLS

Fig. 6 Verification of ULS

Fig. 7 Constitutive law in tension

Session 1

421



6/8

Figure 10 demonstrates the load and deflection

relationship in the middle span obtained from non-linear 3

dimensional FEM analyses considering finite

displacement for ULS. The major purpose of this analysis

is to verify the bridge safety as well as to determine how

many deviators should be installed for ULS. Therefore the

successive loading control method is employed for non-linear analysis. The initial load is (D+L+ pre-stressing) and

the load factor K increases successively 1.0 to 0.5 where

K is defined by K(D+L). The modeling of the structure is

that the web and the flange are modeled by shell

elements, the anchorage for tendons is

modeled by solid elements and pre-

stressing tendon is modeled by truss

elements. K=1.7 means the ULS load. The

judgment for ultimate load is whether the

compressive principal strain exceeds 0.3%

or the tensile principal strain exceeds 0.1%.

Two different cases are calculated; that is(case-1): three deviators (middle + both

sides) are considered, (case-2): seven

deviators (middle + three each side) are

considered. The ultimate load capacity by

case-1 shows about 15% less than one by

case-2. The final decisions for the deviator

installation are taken case-2 according to

this results and those arrangement of the

deviators are almost equivalent to the full

inner pre-stressing cable system.

4. CONSTRUCTION EXPERIMENTS

FOR VERIFICATION

4.1 Mixing, casting and curing

Various kinds of mixing and casting

experiments using the molds for beams,

plates and shells have been carried out

considering the control of the fiber

orientation. Before producing the

prototype pre-cast segment blocks, the

verification experiments of mixing,

casting and curing have been conducted

to make the prototype scale specimens

for the verification loading experiments;i.e. one specimen is similar to segment

block 3L or 3R, another specimen is

similar to segment block 2L or 2R. The

segment blocks 3L or 3R are composed

of two symmetrical blocks that are

divided half at the center of the cross

section. Therefore, two symmetrical

blocks should be connected together by wet joint with 30mm width and lateral pre-stressing before

connecting with segment blocks 3L and 2L.

The type of the mixer is a pan type with 45kW motor and its volume capacity is 1.75m3. Half segment

block 3L was cast into the metallic mold using hopper and tremie method. The segment specimen block

2L was also cast in the same way into the metallic mold. The mold for specimen block 2L has some

circular holes in the web and its holes are made from sthylene foam. The inner mold for specimen block

2L is fixed with the outer mold by bolts through the circular holes. Photo 2 demonstrates the segment

Fig. 8 Constitutive law in compression

Fig. 9 Longitudinal stress distribution

Fig. 10 Load factor and deflection


422


7/8

specimen block 2L for the load carrying experiment.

After preliminary curing was performed for 48 hours at 30oC, the segment specimen was released

from the metallic mold and it was continuously performed 48 hours heat treatment at 90oC. The

segment specimen 3L being connected by wet joint and lateral pre-stressing, it was longitudinally pre-

stressed by two sets of big 31S15.2 tendon, where one tendon was sustaining 3,700kN/tendon by

force.

4.2 Wet join

The wet joint in comparison with the dry joint does not need the match cast process in producing

pre-cast segment blocks. The past records of wet joint are not so many, so it is necessary to verify the

construction process and the structural performance. Photo 3 indicates just after jointing laterally two

symmetrical blocks by 1S12.7 mono-strand, that supplies about 100kN/tendon pre-stressing force. The

gap of wet joint is 30mm and Ductal is poured inside the gap. Both end of the connecting surface to the

pre-cast blocks possess a couple of shear cotter to transform shear force each other.

5. STRUCTURAL LOADING EXPERIMENT

5.1 Anchorage loading experimentThe anchorage for longitudinal pre-stressing is about 0.55m in depth, 1.2m in width and 1.0m in

length. It is surprising that there is no passive reinforcement by steel rebars and furthermore the size of

the anchor plate for 31S15.2 tendon is reduced about 21% in length from the standerd plate. The pre-

stressing anchorage for ordinary pre-stressed concrete is usually reinforced so heavily that casting

concrete and rebars reinforcement becomes difficult. The mass of the anchorage is post-tensioned in

transverse direction by mono-strand to counterbalance the tensile stress due to bending. However the

secondary tensile stresses in the anchorage are directly withstood by the steel fibers in the matrix. The

verification experiment for new size of anchor plate for 31S15.2 has been conducted. Three-

Fig. 11 Prototype specimen for loading experiment

Photo 2 Segment block 2L Photo 3 Lateral wet joint

Session 1

423



8/8

dimensional FEM analysis and the loading experiment also have been conducted to verify the

anchorage can withstand for the pre-stressing forces without any cracks.

5.2 Loading experiment

In order to clarify how the shear cotter work

for shear transfer in the wet joint, the pure

shearing loading experiment has been carriedout. It was found that the frictions between

segment edge and joint material are good

enough to transfer the design shear force.

Next, the bending and shearing loading

experiment has been conducted using I-

shaped pre-stressed beams to clarify the

failure mechanism of wet joint. It was observed

that small shear cotters had better be installed

in wet joint to increase the ultimate shear

loading capacity, as well as to increase the

ductility.

The bending and shearing loadingexperiment for the prototype pre-cast block 3L

as shown in Fig.11, has been carried out to verify the crack behavior for SLS and the ultimate load

carrying capacity for ULS. The experimental results are illustrated in Fig. 12. One of the major purposes

of this experiment is to check the shear resistant given by equations (1) to (4). There are no

observations of cracks for SLS. The ultimate strength was 2,500kN (ultimate shear force=1,250kN) that

was about 1.8 times for the load by ULS. The final failure mode was shear destruction.

6. CONCLUDING REMARKS

Unique and exceptional design has been proposed taking into account of full advantages of material

characteristics, which has never accomplished by the ordinary pre-stressed concrete. It makes it

possible to reduce the dead weight to 1/4 compared with the ordinary concrete and this will extremely

reduce the size of the pier foundation, hence the total cost will be 8~10% reduced.Through the various kinds of material and structural experiments, the fundamental design method

has been clarified and the design result has been verified. Sakata-Mirai Footbridge is now under

construction and it will be completed in September 2002. It should be noted that the design and

construction management rules for Ductal should be further developed through the actual construction

process in the future. From the point of view of the life cycle cost, the long term monitoring of this bridge

is also necessary to accumulate the field data of durability.

This project has been proceeded under the judge and the recommendation by Technical Committee

of Bridge Construction Applying New Material (chairman: Prof. Ikeda, Yokohama National University)

organized by Co-operative Council of university-government-company in Shounai County sponsored

by Yamagata prefecture. We deeply express our gratitude to the people involved in this project.

REFERENCE

[1] Adeline, R., and Cheyrezy, M. : The Sherbrooke Footbridge : the first RPC structure, FIP 98,

Amsterdam, May 1998.

[2] Etienne, D., Causse, M. and Behloul, M. : Design and building of Seoul Peace Footbridge, Third

International Arch Bridge Conference, Paris, pp. 865-876, Sept. 2001.

[3] Cheyrezy, M. : Structural applications of RPC, Proc. of the International Conf. New Technologies in

Structural Engr., Lisbon, Vol.1 pp.5-14, July 1997.

[4] Behloul, M. : Design rules for DUCTAL pre-stressed beam. Technical Information from Bouygues,

pp. 1-15, Feb. 2000.

Fig. 12 Experimental result


424

25 Iunie 09 Sakata Footbridge

Documents

Transcript of 25 Iunie 09 Sakata Footbridge