Design of Piles and Cylinders for the Supports of Docks

continuation for Design of Pier:

General Design

- Determine support condition at both the top and bottom

- In dock construction - piles are designed as LONG columns

- The piles may be considered "fixed" if its ends are prevented from rotating (meaning that for a vertical pile, the axis of the pile must remain vertical at its ends

For Fixity at top of pile:

1. Deck must be of heavy construction and that the pile be rigidly fastened to the deck either by embedding it (if H-Pile) or by extending the reinforcement into the supporting cap or girder(if a concrete pile)

For fixity at bottom at a point not too far below bottom:

1. The soil must be a firm material such as compact sand or hard clay into which the pile is driven a substantial distance between the point of fixity (assumed to be 10 to 15 ft below the bottom)

2. For soft bottom such as silt, point of fixity at 20 to 25 ft below bottom; assume supported from buckling at 5 to 10 ft below bottom (most soils even though of relatively low strength will provide sufficient support to prevent pile from buckling

3. For firm materials and bearing depth is not deep enough to attain the assumed point of fixity, the pile may be assumed to be supported from 0 to 5 ft below the bottom

4. For soft rock, hardpan, or hardclay, the support may be taken at the surface

5. For other materials taht are less dense and may be eroded or disturbed near the sruface, point of support should be assumed 5 ft below the bottom

Various Conditions of Fixity (see fig. 5.21)

- with both ends fixed, the effective length of the pile is taken to be 0.5 of its lenghts between the points of fixity

- if piles are fixed at the top and not at the bottom (for hard materials where point of fixity was not reached), effective length =0 .75 of length figured from the point of fixity at top to teh point of support at the bottom

- if the deck is light construction (wood or light steel) the top of the pile cannot be considered as fixed: effective length = distance between the point of support at the top (underside of the deck) and the point of support at the bottom. Once the effective length is determined, the allowable load may be figured.

Precast-Concrete Piles

- provide a very prmanent type of construction, even in salt water, even without maintenance (if properly constructed and driven)

- limitations in length : handling stresses and weight becomes excessive for very long piles

(prestressing provide longer lengths)

- not recommended for clay soils which lose strength when remolded because a solid concrete pile will displace an equal volume of soil it will disturb and remold clay soils which may result in a considerable loss in shearing strength and frictional resistance to support pile

Design of Axially Loaded RC columns

SHORT COLUMNS

- for effective length, l <> , maximum allowable pile load

P = 0.8 Ag (0.225 f'c + fs pg)

where:

p = max allo pile laod in lb

Ag = gross area of tied column in sq.in.

f'c = comp strength at 28 days, psi

fs = nominal allo stress in vert column reinf. psi

- to be taken at 40 per cent of min spec value of yield point (ex. 16000 psi for 20000 psi int grade steel

- nominal allo stresses for higher yield point may be taken at 40 percent but not less than 30000 psi

pg = ratio of effective c.s.a. of vert reinf in sq.in. to the gross area Ag

LONG COLUMNS

-effective length of pile usually exceed 10 times the least lateral dimension, maximum allowable load P will be reduced to P', max allo load in lb

P' = P (1.3 - (0.03l/t)) where l = effective length or height in inches and t = least dimension

Table 5.2 > Maximum loads in piles varying in size, f'c, and reinf ration from 0.02 to 0.04.

Minimum 0.02 was used eventhough ACI permits 0.01. (reference only. verify with design)

Additional factors to consider in design of piles and thus use lower loads than would be allowed:

1. Piles have to withstand the impact stress from driving

Driving will greatly excede the static stress for which the max pile load is figured; Pile should be driven t oa resistance of three times the design load to provide an adeqaute factor of safety;

Impact stress = Ru/Ag ≤ 0.85 f'c (ultimate strength of concrete

2. There is a maximum resistance to which a pile of a certain weight can be driven with a hammer without damage to the pile.

3. Handling of pile from the casing bed to upright position may cause cracking

reinforcing/handling stress must be kept low to 12000 psi. otherwise, fine cracks may appear; piles must be designed with crack control

Pick-up Points of Piles

two-, three-, or four-point pickup as shown in fig. 22

-steel pipe sleeves are cast in the pile at the pickup points so that the pins cn be inserted to which the wire rope is attached when picking up the piles

-to keep handling stress low to below 12000 psi, long piles must have additional rods at pickup points (weight of pile = 1.25W to consider impact)

- cover = 3 in.

- all corners = 1" chamfer

- bands should be spaced 12in. o.c. except at ends and at pickup points where a closer spacing is required- ---l--long piles will require splicing the main rods (by butt welding or using short splice bars with full tension laps at each side of the splice)

-corner rods shall not be lapped as this requires offsetting the rods

See design example:

* In designing batter piles, the bending stress from the weight of the pile must be combined with the direct stress in determining the safe pile load

fa/Fa + fb/Fb ≤ 1

fa = axial unit sress in lb (actual axial load divided by gross area)

fb = actual unit bending stress due to weight of pile

Fa= allo axial stress P/Ag or P'/Ag

Fb - allo bending unit stress in steel if bending only existing (20000 psi for int grade and 18000psi for structural grade)

Steel Pipe Piles and Cylinders

-Pipes above 24" in diameter is are referred as cylinders

- specified as seamless or longitudinally welded ASTM designation A252 grade 2 (min etnsile strength 60000 psi) or grade 3 (min tensile strength 75000 psi)

- Electric-fusuion-welded spipral-seamed steel pipe, ASTM designation A252, grade 2, not recommended for hard driving conditions

-can be driven either with closed or open ends depending upon soil conditions

- closed ends predominates in marine work and dock construction

- open end piles - for rock or other hard stratum; Skin friction is ignored in figuring the load-carrying capacity of the pile

-close end more economical unless 1) a dispalcement type of pile is not desirable because of loss of shearing strength due to remolding of the soil and 2) a boulder formation exist in which it may be necessary to drill inside the pipe to btain the proper penetration

- pipe piles are filled with concrete except for temporary installations; aside from additional laod caryying capcity, it protects the shell form corrosion from the inside

-for docks, pipe piles are spliced by butt welding using a back-up plat or ring essentially if the pipes are to take uplift or bending

- the allowable closed-end friction loads may be determined as fr H piles (page 324)

Pipe piles or cylinders for dock construction have to be designed as long columns

Allowable load on columns consiting of steel pipe filled with concrete

P' = 0.25 f'c (1-0.000025 * l^2 / Kc^2) Ac + fr' As

where:

P' = allo axial load in lbs

f'c = compressive strength at 28 days

l = effective length of column

Kc^2 = radius of gyration of concrete

Ac = area of concrete

As = area of steel pipe

fr' = allo unit stress i steel pipe (17000-0.485 l^2 / Ks^2 when the pipe has a yield strength of at least 33ksi and an l/Ks ratio equal or less than 120

Ks = radius of gyration of metal pipe section

table 5.9 = max loads at diff effective lengths of pipe piles filled with 3000 psi concrete

Reference: The above are taken from this book unless otherwised referenced to other sources.
DeFQuinn, A. Design and Construction of Ports and Marine Structures. 1972. McGrawHill. p293-298

Design of Piers

Pier - dock which projects into the water; can be used for docking on both sides

Design Considerations

Type of Design

- A pier may be designed as a rigid structure in which the lateral forces are taken by batter piles or by rigid frame action; some movement may still take place due to lateral deformation and bending but is usually ignored in absorbing the impact of the ship

- Some installations - FLEXIBLE to absorb the docking impact (e.g. wood pile clusters because they can absorb energy of impact through the large movement which they are capable of undergoing without permanent distortion - for barges and small vessels only)

- For large vessels, design the pier with structural steel framing and steel piles to provide an adequate resisting force: See Fig. 5.2 and 5.71 for examples.

Loads to be used in Design

-Lateral and vertical loads for which the dock is to be designed:

1. Lateral Loads - from the mooring lines that pull the ship into or along the dockor hold it against the force of the wind or current. (a)

10 psf ≤ Maximum wind force = A * 1.3W ≤ 20 psf (10-20 range taken from wind velocities 55 to 75 mph respectively based on the wind pressure formula p = 0.00256v², multiplied by the shape factor 1.3 where p=pressure in psf and v = velocity in mph)

where: A = exposed area in sq.ft. of the broadside of the ship in a light condition

W = wind pressure in psf (1.3 shape factor; a combined factor taking into consideration the reduction due to height and the increase in suction on the leeward side of the ship.

***

cause of suction on leward side: (for buildings)

As wind blows against a vertical surface of a home such as a wall or steeply pitched roof, it exerts a positive force or “pressure” against that surface. As the wind flows over or around the home, it exerts a negative force or “suction” on the walls or roof planes parallel to or away from the direction of the wind. The combination of these pressure and suction forces can result in the following damaging effects to structures: Uplift; Sliding ; Overturning ; Racking

source: Federal Emergency Management Agency

***

! For 2-sides berthing : the total wind force acting on he pier shall be increased by 50% to allow for wind against the seconf ship

Maximum of 20 psf was ideally established by the author because a ship would not remain alongside the dock in a light condition, in a storm approaching hurricane intensity. The ship would either put to sea or take on ballast to reduce its exposed area to the wind.

!"Ballast is seawater taken in by a ship to keep it stable as it unloads cargo. The ships take in the water at one port and releases it at another" http://www.jamaicaobserver.com/news/html/20041004T230000-0500_67114_OBS_BALLAST_WATER_FROM_CARGO_SHIPS_A_BIG_THREAT.asp

(b) Wind against the pier structure and a warehouse or transit shed on a pier may be a more severe condition than wind on the ship as the sruface area may be larger and the wind intensity is greater. Wind pressures for this case shall be determined for the max velocity in the area and applicable shape factor ranging from 1.3 to 1.6 e.g. in a hurricane area, wind velocity = 125 mph, and total wind pressure = 64 psf

(c)Force of the current (F) = (w/(2g)) * v² : for salt water F = v²

where F = in psf

w = weight per cubic foot of water

v = velocity of current in fps

g = 32.2 ft/s²

The velocity of current is usually 1 and 4 fps which will result in a pressure of 1 to 16 psf

This force F will be applied to the area of the ship below the water line when FULLY LOADED. since the ship

is generally berthed parallel to the current, this is seldom a controliing factor.

2. Docking Impact - caused by the ship ship striking the dock when berthing

Desing assumptions:

(a) Maximumm impact when ship is FULLY LOADED (displacement tonnage) striking the dock

(b) at an angle 10 degrees with the face of the dock

(c) velocity normal to the dock = 0.25 to 0.5 fps

A few installations habe been designed for 1 fps but this is considered excessive, except for small ships, as this corresponds to velocity of approach = 3.5 knots at an angle 10 degrees and could damage the ship

Fender systems - designed to absorb docking impact; resulting force to be resisted by the dock will depend upon the type and construction of the fender and deflection of the dock (if designed as flexible structure)

3. Earthquake Forces - consider if pier is within an area of seismograph disturbance. Horizontal force may vary between 0.025 and 0.1 (verify if seismicity map) of the acceleration of gravity g times the mass, applied at its center of gravity which can be expressed as 0.025 to 0.10 of the weight (g * mass = weight) respectively

Weight to be used = total dead load plus one half of the live load

Unless the dock is of massive or greavity type, the effect on the design will usually be small as the allowable stresses when combined with dead and live load stresses may be increased by 33 1/3 percent.

If batter piles are used to carry the horizontal earthquake force: this must be checked to see that they will carry the horizontal earthquake force without increasing the allo loaing by more than 33 1/3 %, otherwise addtl piles will be needed. (applies to both transverse and longitudinal directions of the pier.

4. Vertical Loads

(a) dead load - dead weight of the structure

(b) live load - usually consists of a uniform load plus wheel loads from trucks, railroad cars or locomotives, cargo-hndling cranes, and equipments; range (250 to 1000 psf of deck area, 250 can be used for oil docksor similar structures where materials are handled by pipelines; usually piers are designed from 600 to 800 psf. used 1000 psf for piers handling heavy metals such as copper ingots and containers)

The uniform live load will control the design of the piles and pile caps, whereas the concentrated wheel loads, including impact will usually control the design of the deck slabs and beams

A reduction of 33 1/3 % is sometimes made in the uniform live load in figuring the pile loads and in designing the pile caps or girders based on the assumption that the entire deck area of adjoining bays will not be fully loaded at one time

Reference: The above are taken from this book unless otherwised referenced to other sources.

DeFQuinn, A. Design and Construction of Ports and Marine Structures. 1972. McGrawHill. p293-298

Marine Structures Definition of Terms

Definition of Terms

Dock - a general term used to describe a marine structure for the mooring and tieing up of vessels, for loading and unloading cargo, or for embarking and disembarking passengers
- referred to as pier, wharf, bulkhead or in European terminology, a jetty, quay, or quay wall

Wet Dock - in Europe, docks are knows as wet dock due to large variations in tide level; an artifical basin for vessels

Dry Dock - artificial basin where the basin is pumped out'

Wharf or Quay - a dock which parallels the shore; generally contiguous with the shore; used for docking at one side only

Bulkhead or Quay Wall - a dock which parallels the shore and is backed up by ground; it supports/holds the ground in back of it

Bulkhead - installed to retain the made ground which is at higher elevation than the waterway; this is done in cases where plants need to be built adjacent the shoreline where the marshy soil will be filled by dredging the adjacent waterway

Bulkhead wharf - part of a bulkhead used as a wharf for docking vessels by addition of mooring apurtenances, paving, and facilities for handling and storing cargo

Pier or Jetty - dock which projects into the water; sometimes referred to as a mole; can be used for docking on both sides; may be more or less parallel to the shore and connected to it at right angles to the pier through mole or trestle (referred as T-head pier or L-shaped pier depending on the approach if at center or at end)

Breakwater Pier - a pier or jetty combined with breakwater;

Dolphins - maritime structures for mooring vessels; used in combination with piers and wharves to shorten the lengths of the piers and warves; principal part of fixed-mooring-berth type of installation used extensively in bulk cargo loading and unloading; also used for tying up ships and for transferring cargo from one ship to another when moored along both sides of dolphins; TWO TYPES : BREASTING and MOORING

BREASTING DOLPHINS - larger than mooring; designed to take the impact of the ship when docking and to hold the ship agaisnt a broadside wind; provided with fenders to absorb the impact of the ship and to protect the dolphin and the ship from damage; usually have bollards or mooring posts to take the ship lines, particularly springing lines for moving the ship along the dock or holding it against the current

Mooring dolphins - additional dolphins installed provided off the bow and stern , located some distance in back of the face of the dock; privided because the springing lines are not very effective in a direction normal to the dock, particularly when the ship is light; provided to hold the ship against broadside wind blowing in a direction away from the dock; not designed for the impact of the ship as they are located in back of the face of the dock where they will not be hit; effective when installed about 45 degress off the bow and stern and mooring lines will not be less than 200 ft nor more than 400 ft long and when only two will be used; largest ships may require additional 2 dolphins off the bow and stern and these are located so that mooring lines will be normal to the dock which makes the most effective in holding the ship against offshore wind; provided with bollards or mooring posts and with capstans when heavy lines are to be handheld;
maximum pull on single line may not exceed 50 tons or 100 tons on a single bollard if two lines are used

Fixed mooring berth - marine structure consisting of dolphins for tying up the ship and a paltform for supporting the cargo-handling equipment; platform is set back 5 to 10 ft from face of the dolphins so that the ship will not come in contact with it, and therefore does not have to be designed to take the impact of the ship

Moorings for ships - consist of ground tackle placed in fixed positions for attaching the ship's lines; each unit consist of one or more anchors with chani, sinker, and buoy to which the lines are attached; these are located so as to take the bow and stern lines; one or more breasting lines are needed for large ships; for some moorings where the wind is in one direction, the ship may use its own bow anchor and the fixed tackle off the bow may be omitted

References:
DeF Quinn, A. Design and Construction of Ports and Marine Structures. New York, 1972. page 265-267.

Design of Submerged Tanks With Water Table (Tipping Pits)

In design of submerged tanks with detected water table, FLOTATION must be checked aside for stability and overturning. Check for flotation can be done by considering an uplift force caused by the buoyant force. The factor against flotation can be computed by dividing the Total Dead Weight (DWT) of the tank by the Buoyant Force (BF). BF is the weight of the volume displaced using the unit weight of water = 9.81 kN/cu.m from the level of the water table. Acceptable factor of safety against flotation = 2.0 but a 1.5 FS can be deemed acceptable depending on professional judgment.

Nestle Cabuyao Egron Building

This is another project with numerous revisions. I finished this first around mid-2008.

Scope:

New equipments within Egron Building
Additional Access left of the building

Things I've learned:

1. Retrofitting of existing concrete columns/girders can be done by:
a. providing 45 degree - knee braces
b. providing diagonal knee braces
c. providing vertical knee braces
d. providing vierendeel trusses
e. providing intermediate steel beams

2. There are instances where I was asked to "release" the ends of overstressed girders (considered hinge) as "it will develop a plastic hinge when loaded" as per my boss. I researched over the net about plastic hinge:

"In structural engineering beam theory the term, plastic hinge, is used to describe the deformation of a section of a beam where plastic bending occurs.

Plastic behaviour
In plastic limit analysis of members subjected to bending, it is assumed that an abrupt transition from elastic to ideally plastic behaviour occurs at a certain value of moment, known as plastic moment (Mp). Member behaviour between Myp and Mp is considered to be elastic. When Mp is reached, a plastic hinge is formed in the member. In contrast to a frictionless hinge permitting free rotation, it is postulated that the plastic hinge allows large rotations to occur at constant plastic moment Mp.
Plastic hinges extend along short lengths of beams. But detailed analyses have shown that it is sufficiently accurate to consider beams rigid-plastic, with plasticity confined to plastic hinges at points. While this assumption is sufficient for limit analysis, finite element formulations are available to account for the spread of plasticity along plastic hinge lengths[2].
By inserting a plastic hinge at a plastic limit load into a statically determinate beam, a kinematic mechanism permitting an unbounded displacement of the system can be formed. It is known as the collapse mechanism. For each degree of static indeterminacy of the beam, an additional plastic hinge must be added to form a collapse mechanism." (Wikepedia.org)

3. Overstresses up to 3.0 on footings can be accepted but with risks involved. Damage can be rapairable. Also, diagonal braces can be placed throwing the column loads on nearby footings and release the column with diversion braces. Columns can also be assigned as "hinged" by making the existing column to baseplate connection as "hinged"

4. Overstresses up t0 1.25 on concrete columns and girders were accepted. Better use 1.2.

Nestle Pulilan Ice Cream Plant

It's been a long time since my last post. Well, I have been busy with the numerous revisions in my recent project - NPI Pulilan Ice Cream Plant. Now, it's almost finish and and I just need to revise few things and include the piperacks.

Things I've learned while doing the design:

1. Increase in roof height of 2.0m (from el. 6.4m to 8.4m) increases wind loading by about fifty percent. New roof trusses and truss retrofitting are smaller considering the 6.4m height than the 8.4m.

2. Retrofitting top chords without roof raising can be done by providing L-plates forming a box with the angular or wt top chord.

3. Use stitch welds for cover plating the whole length of top chord as continuous weld will cause warping of members. (50mm @ 150mm o.c.)

4. When using rafters instead of trusses, the edges can be tapered by maximum 600mm.

Retrofitting of Existing Building

It's been a while since my last post. I have been busy with a huge project which involves a lot of retrofitting works. It is