Modelling of sheet pile walls

Sheet pile walls are usually discretised with structural elements (beam or shell elements). This type of discretisation can lead to problems if under vertical loading a signi ficant part of the load is carried via the base of the wall. In the case of individual sections, an extension of interface elements can be taken into consideration at the base of the wall so that the sheet piling section can penetrate into the ground and no unrealistic stress peaks can occur in the body of soil below the base of the wall – see recommendation E4-15 in (S CHANZ, 2006). In the case of combined sheet pile walls under vertical loading where significant bearing pressures are mobilised, a bearing pressure can be modelled with the help of a stiff transverse beam at the base of the wall (MEISSNER, 2002).

In the case of a staggered sheet pile wall, the 2D equivalent model must take into account the fact that the base of the equivalent wall is permeable.

Where possible, the force transfer between sheet pile wall and soil should be modelled with interface elements or by way of kinematic contact formulation. This guarantees that no tensile stresses are transferred along the sheet pile /soil boundary surfaces and that, with corresponding action effects, irreversible sliding between sheet pile wall and soil can take place. Bilinear contact and friction principles are used for this in the simplest case.

Simulation Of The Construction Process

Initial state of soil

A steady-state earth pressure (K 0 -state) is normally assumed. This is, however, linked to var- ious conditions (H ÜGEL , 2004). It should not be forgotten that the steady-state earth pressure coef ficient K0 depends on the loading history of the soil. Initial values for pore water pressures and excess pore water pressures can be determined from in situ measurements. Initial values for the in situ density of the soil can be specified by penetrometer tests or, in the case of high-quality material models, in conformity with their compression law.

Simulating construction processes

The majority of published finite element projects do not include any simulation of the instal- lation of the sheet pile wall, but instead the corresponding elements are activated in their final position in the finite element model. This technique is often referred to as wished-in-place.The changes to state variables and stresses and strains in structures due to the construction process are therefore ignored. However, these may be relevant, especially where problems with small deformations occur (HÜGEL , 1996; VONW OLFFERSDORFF, 1997). Currently, the simulation of the construction process is restricted to university facilities because only they have the necessary hardware and software. In practice the construction processes are usually not simulated.

Material failure of components

Verification of the loadbearing capacity of the steel sheet pile section can be carried out via an elastic analysis of the permissible stress. This corresponds to the EAB method for excavations and the EAU method for waterfront structures. However, current research into the determination of the ultimate load capacity Rd,i of steel sheet piles at the ultimate limit state enables the advantages of plastic design to be exploited for sheet pile walls as well. Information on the plastic method of analysis can be found in K ALLE, (2005) and DIN V ENV 1993-5 (1998).The follow example shows the design for the elastic-elastic case to DIN 18800 (1990).

Example: Simpli fied analysis of material failure of sheet pile wall to DIN 18800-1 (1990)

The analysis of material failure of the sheet pile wall is carried out for the system shown in example 6.10 and 6.11.

From the structural calculations we get the following actions:

due to permanent loads due to variable loads design value
Resultant anchor forceA [kN /m] 109.3 23.1 182.2
Horizontal equivalent force C [kN /m] 91.6 10.6 139.3
Bending moment Mmax [kNm /m] 162.7 27.9 248.7
Normal forceNmax [kN /m] -68.9 -11.5 -110.4

Requirements for the material resistances can be found in the respective standards.

Select:    HOESCH 1605 section

steel grade S 240 GP, min. yield strength fy,k = 240 N/mm2

Partial safety factor to DIN 18800: γM=1.10

For simplicity, the comparative stress analysis for the maximum design loads M maxand Nmaxis carried out, the shear stress analysis will be neglected.

The limit condition to DIN 1054:2005-01 is rewritten for the limit condition regulated in the standard. In the case of verifying the sheet pile wall section

Ed ≤ R M,d   becomes   σd ≤ fy,d

The following applies

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The analysis is satisfied; the degree of utilisation of the section amounting to μ = 75% may be optimised if
required.

Material models for soils

The choice of thematerial models for soils is limited in some finite element programs. The material models of the “linear elastic, ideal plastic” category can lead to incorrect predictions in the case of retaining wall structures – see, for example, (HÜGEL , 2005), (V ERMEER & W EHNERT, 2005) and recommendation E3-4 in (S CHANZ, 2006). The use of high-quality elastoplastic or hypoplastic material models is called for which can at least describe the main phenomena of the mechanical behaviour of soils:

  • stiffnesses not dependent on pressure,
  • different stiffnesses for unloading and reloading,
  • shear behaviour for drained and undrained conditions,
  • dilatancy behaviour.

For a detailed explanation of the main phenomena of the mechanical behaviour of soils, see, for example, (H ERLE &MAŠÍN, 2005) or (SCHANZ, 2006). High-quality material models may even be necessary during the feasibility studies for sheet piling structures.

Selected results from thefinite element

Selected results from thefinite element analyses can be summarised as follows:

  • Loading: In state 7 the finite element analysis indicates irreversible deformations due to the variable load q . According to DIN 1054:2005-01, the variable load should therefore be taken into account when checking the serviceability of the structure in the finite element model.
  • Earth pressure distribution: As expected, at the serviceability limit state the passive earth pressure is lower than that given by the calculations in example owing to the flexibility of the retaining wall. The active earth pressure is greater in thefinite element analysis . 20150715 86
  • Support at base of wall : The moment distributions calculated confirm that with an em-bedment depth of 4.8 m in the soil, the base of the sheet pile wall is partially fixed. 20150715 85
  • Deformations: As expected, the deformations of the sheet pile wall correspond to a flex-ible installation, the anchors yield. The large wall displacement causes corresponding settlement of the ground surface on the land side, a maximum inclination of approx. 1:80 occurs . During the construction phase, the deformations do not represent a problem for quay structures. When in service, the depression caused by the settlement can be compensated for by backfilling so that the area is traf ficable, e.g. for stacking containers. 20150715 87

Other possible issues for this boundary value problem might be the long-term behaviour of the quay structure due to other actions, the change in the water table over time and viscous processes in the stratum of clay with sea-silt. To do this, the finite element model described here would need to be adjusted with respect to the material model and the identification of parameters.

Sheet Piling Structures

The choice of thematerial models for soils is limited in some finite element programs. The material models of the “linear elastic, ideal plastic” category can lead to incorrect predictions in the case of retaining wall structures – see, for example, (HÜGEL , 2005), (V ERMEER & W EHNERT, 2005) and recommendation E3-4 in (S CHANZ, 2006). The use of high-quality elastoplastic or hypoplastic material models is called for which can at least describe the main phenomena of the mechanical behaviour of soils:

• stiffnesses not dependent on pressure,

• different stiffnesses for unloading and reloading,

• shear behaviour for drained and undrained conditions,

• dilatancy behaviour.

For a detailed explanation of the main phenomena of the mechanical behaviour of soils, see, for example, (H ERLE &MAŠÍN, 2005) or (SCHANZ, 2006). High-quality material models may even be necessary during the feasibility studies for sheet piling structures.

Dolphins

General

Dolphins are required in waterways and ports for various tasks: as berthing or mooring dol-phins. Their various functions require an analysis of different actions. Berthing dolphins must be designed for the impact of ships, mooring dolphins are subjected to the pull of mooring lines, wind loads and hydrodynamic pressures.

Dolphins can consist of single piles or groups of piles, the latter usually being met with in the form of lightweight timber piles in old structures. In the form of single piles, steel tubes or compound sections assembled from sheet piles, e.g. LARSSEN steel sheet piles, are to be recommended.

Loads

The critical design loads for dolphins result from the impact of ships during berthing manoeu-vres or the pull on the mooring lines of ships. The latter effect is made up of ship movements due to currents, wind, waves or ice. Berthing dolphins are designed for the ship impact loading case with a force FS,k such that the berthing energy can be converted into deformation work in the dolphin. The energy absorption capacity Ak,exist of a dolphin is calculated from the ship impact force FS and the horizontal de flection f of the dolphin at the level of application of the force:

Ak,exist =1/2 · FS,k · f

The available energy absorption capacity Ak,exist of a dolphin should be selected such that it is greater than or equal to the required energy absorption capacity A. The required energy absorption capacity A describes the component of the kinetic energy of the ship that must be absorbed by the dolphin. This is calculated using the mass, length, speed, turning speed and displacement of the ship, the spacing of the dolphins and the clearance under the keel. An exact description of how to calculate the required energy absorption capacity can be found in EAU 2004 section 13.3.

Subjected to the critical impact action FS , the design value of the steel stresses may not exceedthe yield strength fy in the case of berthing dolphins. For mooring dolphins, the design value of the steel stresses due to line pull, wind loads and water pressure may be equal to the maximum steel stress fu.

Relevant Criteria About Choosing Pile Sections

The following criteria are generally relevant when choosing pile sections:

  1. Dimensions required according to DIN 1054:2005-01 for ultimate limit state (LS 1) and serviceability limit state (LS 2).
  2. Adequate moment of resistance for transport and installation of sheet pile wall Proper support is important during handling on the building site, e.g. attachment of crane slings, because otherwise inadmissible deformation of the sheet pile prior to driving can occur which is not the fault of the fabricator. Furthermore, driving by means of pressing, impact hammer and vibration places severe loads on the pile in some situations. These loads depend on:
    • the length of the pile,
    • the flexibility and position of the pile guides,
    • the method of driving plus the chosen driving parameters (mass and drop height of impact hammer), vibration parameters (amplitude of eccentric weights, frequency, static preload), pressing force in comparison to weight of section,
    • prior deformation of the sheet pile caused by transport,
    • the subsoil, especially type of soil, density in the case of non-plastic soils, consis-tency in the case of cohesive soils, natural obstacles such as rocks plus inclined, hard bearing strata, man-made obstacles such as existing works, and
    • deviations of the adjacent sections and piles (and their interlocks) already driven.

    Owing to the multitude of aforementioned influencing factors, the section is mainly spe-ci fied based on experience.

  3. Adequate material thicknesses taking account of intended service life and expected rate of corrosion. It should be remembered that the zone with the highest corrosion rate does not necessarily coin-cide with the point of maximum structural loading. If conditions are unfavourable or additional protection is required, active or passive corrosion protection measures can be specified instead of a heavier section.
  4. If applicable, planned multiple use of the sheet pile walls taking into account the afore-mentioned aspects

The choice of steel grade essentially depends on the desired steel properties, e.g. with respect to suitability for welding.

For driving and economic reasons, sheet piles are sometimes driven to different depths within the same wall according to R 41 of EAU 2004. A value of 1 m is customary for the so-called stagger dimension, and experience shows that a structural analysis of the longer sheet piles is then unnecessary.

Understanding The Tie Rod Hole Leak Problem

The conventional forming system of concrete walls utilizing tie rods.

The following description supports the understanding of the condition of leaking tie rod holes left from foundation forming systems that use 5/8 (15.88 millimeters) reinforcement rods. Tie rod holes are also commonly referred to as pinhole leaks, rod pocket leaks, and tie backer hole leaks in other regions of the United States. After constructing the foundation wall, these tie rods are removed with the wall forming system, leaving holes in the poured concrete wall. Some newer forming systems that use snap ties instead of tie rods to hold their forms together do not apply to this article.

Poured concrete foundation walls begin with the construction of forms in which to pour the cement. For many years, these forms called shuttering have been constructed from wood that is held together by steel rods called tie rods, tie backs, or tie reinforcement rods. These rods are situated approximately every eighteen inches (0.46 meters) and about five feet (1.52 meters) high from the basement floor across the entire basement. A second row is aligned vertically underneath and about one foot (0.30 meters) from the base of the floor. Basements higher than eight feet (2.44 meters) sometimes will have three rows aligned vertically.

How a tie rod hole is formed.

Once the forms are in place, the tie rods are fastened and support the shuttering which holds the weight and the form of the foundation wall. Once the cement is poured, these forms are left a few days for curing. When that step is accomplished, the tie rods are removed allowing the shuttering to be dismantled. When this step is completed, you are left with a poured concrete foundation. The walls now have holes where the tie rods were that are approximately 5/8 inches (15.88 millimeters) in diameter. In this type of conventional forming system, the tie rods ”(are not)” left in the wall. The only time supporting wall forming ties are left in the wall is when a contractor uses a wall forming system that utilizes (snap ties).

Why tie rods leak after construction.

After the wood forms are removed some contractors will apply hydraulic cement on the outside of the tie rod holes and spray a tar based coating. After a few years this coating will break down and water will begin to enter the holes. Over the years since pouring of foundations began, there have been varying attempts and methods to stop these leaks. Some work for a few years while others fail quickly. Repair contractors have applied a polyurethane caulk and cork method for a quick fix, but years later the leak returns. The leak returns because these methods do not utilize a sealing system that reacts or co-exists with water. Instead, they use methods or products to bond up the hole that will loosen later due to delamination of the product/surface area.

Revealing the tie rod hole from inside.

The inside of the wall is also coated with a trowel applied hydraulic cement to fill in the tie rod hole, then in some cases sprayed over with a white stucco type finish more commonly called structo-lite; a mixture of (Structo-lite and autoclaved Lime). Some builders will not apply this coating which makes it easier to see the location of the tie rod holes. In this case where the white coating is sprayed on, they are harder to see until they begin to leak. Removal of the trowel applied hydraulic cement reveals an open tie rod hole going all the way to the outside of the basement wall. A simple removal of the trowel applied hydraulic cement reveals a hole going through to the soil side where the exterior hydraulic cement has been applied in the same fashion.

Tie rod leaks can cause a lot of water damage in basements.

When tie rods holes begin to leak they can flood and destroy finished basements drywall and carpeting. Tie rod hole leaks have commonly been mistaken as drain tile failure. Due to the amount of water they can allow in it is understandable how this can happen. In some cases the leak is hard to detect since the water coming from the tie rod hole will dry on the wall leaving a puddle on the floor with no traceable evidence of where it came from originally. The photograph below shows a case of one tie rod hole leaking, washing in soil from outside making it easy to trace. The amount of water resulting from this condition is commonly mistaken for drain tile failure.

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Unsealed tie rod holes are entrance for termites, ants and other insects.

Most tie rod holes become an entrance for insects as they use the hole and old cork repair material for a nest as well as being a direct entrance from outside soil.

Repairing tie rod holes before finishing a basement.

If a home owner is planning to finish their basement and it has tie rod holes, they should consider repairing all of them before the installation of the final wall covering. Leaving the holes unsealed will eventually cause future problems behind the drywall or paneling. Below is a photograph showing extensive drywall removal to repair leaking tie rod holes left unsealed when the basement was finished without proper repair methodology for tie rod holes.

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(This article comes from trxplug.com editor released)

H-Beams vs. I-Beams

The differences between an H-beam and an I-beam are very slight. The two beams look very similar in construction and are often called the same thing — a W-beam or wide-flange beam. The beams are often used for different types of construction or different parts of the structure.

Flanges

Both the H-beam and I-beam have top and bottom flanges. The flanges on an H-beam are longer and stick out farther from the center web. The flanges on an I-beam are shorter and not as wide. The distance from the end of the flange to the center web is shorter on an I-beam than the same measurement on an H-beam flange.

Fabrication

Another difference between an H-beam and I-beam is the fabrication method used to make the beams. The I-beam is fabricated by milling or rolling the steel. The size of the I-beam is limited by the capacity of the milling equipment, which this is why I-beams have smaller flanges. H-beams are built up rather than milled, so they can be made any height and width.

Plates

Since I-beams are milled or rolled, the web and flanges have a bevel where the three pieces come together and look like one piece. H-beams have the top and bottom flanges attached to the center web by welding or riveting them together. You can actually see that the H-beam is made of three different metal plates.

Spans

H-beams are useful for longer spans than I-beams because the H-beam can be fabricated to any size. I-beams are good for spans of 33 feet to 100 feet because of the size limitation. H-beams can be used for spans up to 330 feet.

(This article comes from eHow editor released)