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Re: Pier Natural Frequency

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Pier Natural Frequency
• From: TJ_Fu(--nospam--at)URSCorp.com
• Date: Tue, 28 Dec 2004 14:08:24 -0500

```I have been using the following equations for seismic load application to
develop many types of elevated water tank design programs.

Natural Frequency, w = SQRT(K / Mass) = SQRT[K / (W/g)] = SQRT(Kg / W) in

Where, K = Spring constant = P / defl.  in kips/in  (The load that produce
a unit deflection at C.G.)

g = Acceleration of gravity = 386 in/sec^2 = 32.2 Ft/sec^2

W = Total weight of pier and machine in kips

Natural Period, T = 2(pi) / w = 2(pi)SQRT(W / Kg) = 2(pi)SQRT(W / 386 / K)
=- 0.32 SQRT(W / K) in seconds / cycle

T.J. Fu

"Rich Lewis"
<sea@lewisenginee        To:       <seaint(--nospam--at)seaint.org>
ring.com>                cc:
Subject:  Pier Natural Frequency
12/28/2004 12:17
AM
seaint

I have a requirement to have a cantilever pier supporting a machine to have
a natural frequency greater than 50 Hz.  How do you calculate the natural
frequency of a cantilever pier?

Rich Lewis
Lewis Engineering

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