Date resat as 01-01-1970 after update

Hello everyone, 

I am try to update my member profile data & after updated, All dates in form (like Birth day) reset as  01-01-1970. Any one know the solution for this thing. this is my model,

PHP Code:

function update_member($id)
   {
       $now = date_default_timezone_set('Asia/Colombo'); // Set Time-Zone
       $now = date('Y-m-d H:i'); //Fomat Date and time


       $data['custom_member_id'] = $this->input->post("custom_member_id");
       $data['surname'] = $this->input->post("surname");
       $data['other_name'] = $this->input->post("other_name");
       $data['initials'] = $this->input->post("initials");
       $data['title'] = $this->input->post("title");
       $data['gender'] = $this->input->post("gender");
       $data['b_day'] =  date('m-d-Y', strtotime( $this->input->post("b_day")));
       $data['join_date'] = date('m-d-Y', strtotime( $this->input->post("join_date")));
       $data['last_renewal'] = date('m-d-Y', strtotime( $this->input->post("renewal_date")));
       $data['status'] = $this->input->post("status");
       $data['membership_status'] = $this->input->post("membership_status");
       $data['created_by'] = $this->session->userdata("NAME");
       $data['created_at'] = $now;

       $this->db->where('id', $id);
       $this->db->update('membership', $data);


       $b_d['b_date'] = date('Y-m-d', strtotime( $this->input->post("b_day")));

       $this->db->where('member_id', $id);
       $this->db->update('birth_day', $b_d);

   } 


This is my Controller,

PHP Code:

 function update_member_view($id)
    {
        if ($this->session->userdata("NAME"))
        {
            $role= $this->session->userdata("ID");
            if ($role >=1)
            {
                if ($this->input->post())
                {
                    $this->form_validation->set_rules('surname', 'Surname Name', 'required');
                    $this->form_validation->set_rules('other_name', 'Names Denoted by Initials', 'required');
                    $this->form_validation->set_rules('initials', 'Initials', 'required');
                    $this->form_validation->set_rules('b_day', 'Date of Birth', 'required');
                    $this->form_validation->set_rules('address_01', 'Address Line - 01', 'required');
                    $this->form_validation->set_rules('city', 'City', 'required');
                    $this->form_validation->set_rules('zip_code', 'Zip Code', 'required');
                    $this->form_validation->set_rules('mobile', 'Mobile Phone', 'required');
                }
                if ($this->form_validation->run() == TRUE)
                {
                    $this->Membership_model->update_member($id);
                    redirect('membership/member_list');
                }
                $data["row"] = $this->Membership_model->update_member_view($id);
                if ($data["row"] == null)
                {
                    $this->load->view('includes/header');
                    $this->load->view('includes/top_header');
                    $this->load->view('includes/left_nav');
                    $this->load->view('error_page/404');
                    $this->load->view('includes/footer');
                    $this->load->view('includes/settings');

                }else
                {
                    $this->load->view('includes/header');
                    $this->load->view('includes/top_header');
                    $this->load->view('includes/left_nav');
                    $this->load->view('membership/update_member', $data);
                    $this->load->view('includes/footer');
                    $this->load->view('includes/settings');
                }
            }
            else{
                $this->session->set_flashdata('message_name', 'You did not have permission to access this page.');
                redirect('user/index');
            }
        }
        else{
            $this->session->set_flashdata('message_name', 'Your session has been expired. Please Login');
            redirect('login/employee_login');
        }
    } 


Please help me to resolve this error..

date('d-m-Y', 0) = 01-01-1970 ...

Simply this means that there is zero value for date, either this zero comes from DB or from the post, which ever is displayed wrong..

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