FIELD OF INVENTION:

This invention relates to improvements in hydraulic jack for holding a load for a longer period of time extending to many months and year. Modification is made specific to carry out the creep test more efficiently and more robustly. The invention relates to a creep testing machine for testing the deformation of high grade concrete under the influence of stresses.

The present jack is so designed and assembled that the load maybe applied and applied preferably hydraulically and when applied to the desired load, a fixing means such as a screw member and companion unit may be made to engage the body of the jack to support the load, thereby enabling the hydraulic pressure on the hydraulic system from a jack can be released.

OBJECT OF INVENTION:

Higher grade concretes are started using in the construction. However, there is no simple machine is available to test creep characteristics of high strength concrete and have disadvantages like size of the frame, maximum load capacity, adjustments to be done during the test period, etc.

Existing machines are available only for lower grade concretes, and usually they are manually operated. Load drop has to be corrected at regular intervals requires manual intervention. There are some high capacity machines, which built on the principle of the dead weight and lever arm system, which are not useful for high grade concrete tests. Some creep machines use coil springs and use the reactive force of springs as the creep load for the specimen. The load application in such machines is controlled by the size and number of springs. Fine tuning to the required load is complex in such spring loaded system.

Hence understanding such limitations in the existing equipments, suitable instrument is designed to overcome the above limitations to study the high strength concretes, which forms the basis of this invention. It has got advantages of mechanical & hydraulic systems of compactness, computer control, finer load adjustment and power savings.

Draw backs of known art:

a) The existing creep testing machine for high grade concretes are too large and expensive for routine use.

b) Existing simple creep testing machines are suitable only for lower grade concretes

c) Engineer attention is required for monitoring the test.

d) Existing creep testing machine for high grade concretes requires more space in the lab.

e) Skilled instrumentation engineer required for instrumentation preparation.

An object of this invention is to provide a combination of hydraulic lifting mechanism and a mechanical holding mechanism to hold a load with a hydraulic system to carryout creep test.

An object of this invention is to apply load on the specimens by hydraulic lifting mechanism and a mechanical holding mechanism to hold a load within specific tolerance level required to carry out creep test

Another object of the invention is to provide combination of a jacking mechanism and a holding mechanism whereby a load may be lifted hydraulically and retrogression of the hydraulic piston/ ram is obviated by mechanical means.

Still another object of the invention is to provide a combination of a hydraulic jacking and holding system which embodies a hydraulic ram for lifting a load, with a clamp force applied with clamping ring thereon to receive a locking means to hold the load without strain on the hydraulic system.

Still another object of the invention is to provide a hydraulic jacking and holding system which embodies hydraulic ram for lifting a load, clamp force applied with clamping ring thereon to receive a locking means which is clamp to hold the load without a need for the hydraulic system.

Still a further object of the invention is to provide a unitary hydraulic jack with a clamping ring thereon for lifting a load hydraulically and for holding the load in a creep testing machine.

The another object is to develop a simple, accurate and fully automated testing machine to study the creep properties of wide ranges of concrete grade and it is based on the principle that the material is subject to constant compression load through force through hydraulic jack.

With these objects in view and others which will become manifest as the description proceeds, reference is to be had to the accompanying drawings.

DESCRIPTION OF INVENTION

The invention is a creep testing machine and a portion of hydraulic system is illustrated in fig 1.

Maintaining load constant with a regular hydraulic jack or hydraulic actuators with closed loop system or lever arm systems are inefficient in various aspects like requirements of oil leakage, oil volume expansion due to temperature, uninterrupted high power, huge space, high maintenance and safety etc.

A creep testing machine is developed to study the creep characteristics of the concrete specimen. The creep characteristics at sustained load are an essential data to design many sensitive and complex reinforced concrete structures.

There are four major parts in this machine. They are loading frame, hydraulic actuator, hydraulic power pack unit and data acquisition system. The loading frame consists of four columns and two platens. The platens are located at top and bottom and its positions are locked in the treaded portion of the frame by lock nuts. Three concrete cylinders of 150 mm diameter and 300 mm height specimen can be tested at a time. Force application is done using the hydraulic actuator. The actuator is pressurized through the power pack unit or hand pump.

The hydraulic power pack unit consists of oil tank, pressure control valve and electronic DAQ boards for precise load control. Software is developed for controlling this testing machine to apply the force and monitor through computer. Load measurement is derived through the pressure transmitter, which is calibrated against load cell. Free space in the frame allows accommodating external load cell. Strain measurements are done through extensometer.

Fig 1 - Complete setup of creep testing machine

Fig 2 - Hydraulic power pack unit

Fig 3 - Line diagram of loading frame & Hydraulic power pack of creep testing machine

Fig 4 - Front view of Hydraulic Cylinder with clamp

Fig 5 - Top view of Hydraulic Cylinder

Fig 6 -Block diagram of creep testing machine

Fig 7 - Customized Hydraulic actuator

Having thus clearly shown and described the invention, what is claimed as new and desired to be secured is a hydraulic lifting jack and clamping load holding mechanism which is characterized with a mechanical lock as clamping mechanism. Wedge mechanism known in many prior art is integrated part of hydraulic cylinder and it works with screw type piston only. Whereas clamping mechanism in the invention is an add-on part and it is not limited only to screw type of piston. It can be used flexibly in plain piston and any type of piston with suitable modifications in clamp.

The parts of the inventions are:

• 1000kN Loading frame is consists of top & bottom steel plates, which are connected to four steel columns & mesh guard arrangement on all four sides for human safety during operation. The position of the top plate can be adjusted to the required height and locked with steel nuts. At a time three 300 mm height & 150mm diameter concrete cylinders can be tested for creep characteristics.

• Hydraulic Actuator: It is a precise customized hydraulic cylinder, which is fixed in the bottom of the 1000kN loading frame. A clamping ring was devised to control the load drop of actuator and to maintain the load constantly. This arrangement eliminates continuous pumping of oil through the pump. Minor adjustment beyond the load drop of ±1% of load can be intervened easily by precise hydraulic controller. This arrangement saves power and frequent manual intervention.

• Figure 3 & 4 - shows the hydraulic cylinder with clamping ring attachments. Once the required load is applied on specimen using hydraulic pump, the piston can be locked in its current position by tightening the clamping ring. So that the applied load will be maintained for longer duration of time even if hydraulic pressure is released.

Clamping ring can be clamped on piston by tightening the locking screw. If the locking screw is tightened, the clamping ring gets clamped with piston in its position and downward movement is arrested in both on & off of hydraulic pressure. If the locking screw is loosened, Clamping ring will get undamped from piston and offer no resistance to piston movement in either direction.

• Load measuring sensor: Digital load measuring sensor is fixed in the top plate for the measurement of applied load on a specimen, and it is interfaced to an electronic controller to give a feedback command. For cross verification of pressure transmitter and off pressure during mechanically load holding period, the external load measuring sensor like reference proving ring or digital load cell is used.

• Hydraulic power pack with pressure transmitter: It consists of oil tank, solenoid valves, pressure control valve and pump. The pressure transmitter is located on pressure line and the analog signal is converted into digital by the electronic controller.
• Electronic controller: It is customized digital controller consists of relays, contactors and data acquisition system to control the pressure control valve, oil flow of hydraulic actuator. It will switch contactors, and relays on & off to adjust the load suitably. It also measures load and transfers the data to PC/laptop via USB interface.

• Computer & Creep Software: It communicates user commands and control parameters to electronic controller via USB port.

The creep testing apparatus for testing concrete specimen is one aspect of the invention comprises a frame comprising of four columns, a top plate and a bottom plate. The top plate is preferably slidably adapted onto the frame for sliding in a vertical direction towards and away from the bottom plate. It is removably fixable at given heights on the frame. It also has a hydraulic actuator means with a piston that is reciprocally movable inside a cylinder between a first and a second position of the piston. In the first position the piston is disposed towards the bottom plate that is piston goes back in to the cylinder. This movement is possible only if the piston is already extended out from its home position of the cylinder and in second position the piston is disposed towards the top plate. Further the said hydraulic actuator means is mounted on the bottom plate of the frame for applying and controlling the force on the material to be tested. A metal clamping ring means mounted on the hydraulic actuator means alongwith a locking screw is provided for mechanically locking the piston in the second position of the piston for controlling the load drop of the actuator and maintaining the load constant. Further a load cell means is removably mounted on the top plate of the frame and adapted to abut against the test material for detecting force applied thereon by the actuator. The load cell will provide a signal corresponding to the force detected. A displacement signal detection means is provided for processing the strain experienced in the specimen over the period of time at constant load. A feedback control means is operably associated with hydraulic actuator means and load cell means to maintain continuously a constant sensed force on the specimen.

In another aspect of the invention, the creep testing apparatus comprises of the top plate and the bottom plate of the frame configured to hold the test material therein between.

In another aspect of the invention, the creep testing apparatus comprises of the feedback control means which may be an electronic controller.

In another aspect of the invention, the creep testing apparatus comprises of the feedback control means which may further include necessary visual displays and appropriate operable buttons and switches.

The described assembly and the structure produces the necessary result for a creep testing machine, but it is obvious that changes may be made in various structural and component elements disclosed herein to meet different requirements. Hence no limitation is implied by the specific description other than which may be required by the claims.

WE CLAIM:

1. A creep testing apparatus for testing concrete specimen comprising of:

a. a frame comprising of four columns, a top plate and a bottom plate, wherein the top plate is preferably slidably adapted onto the frame for sliding in a vertical direction towards and away from the bottom plate and removably fixed at given heights on the frame,

b. a hydraulic actuator means with a piston that is reciprocally movable inside a cylinder between a first and a second position of the piston, wherein In first position the piston is disposed towards the bottom plate and in second position the piston is disposed towards the top plate, the said hydraulic actuator means is mounted on the bottom plate of the frame for applying and controlling the force on the specimen to be tested,

c. a metal clamping ring means mounted on the hydraulic actuator means alongwith a locking screw for mechanically locking the piston in the second position of the piston for controlling the load drop of the actuator and maintaining the load constant,

d. a load cell means removably mounted on the top plate of the frame and adapted to abut against the test specimen for detecting force applied thereon by the actuator, the load cell providing a signal corresponding to the force detected,

e. a feedback control means operably associated with hydraulic actuator means and load cell means to maintain continuously a constant sensed force on the specimen, and f. a displacement signal detection means for detecting the strain experienced in the specimen over the period of time at constant load.

2. The creep testing apparatus as claimed in claim 1, wherein the top plate and the bottom plate of the frame configured to hold the test material therein between.

3. The creep testing apparatus as claimed in claim 1, wherein the feedback control means may be an electronic controller.

4. The creep testing apparatus as claimed in claim 1, wherein the feedback control means may further include visual displays and operable buttons and switches.